the resin composition of the present invention is necessary to contain flat glass fibers . the flat glass fibers in the present invention represent glass fibers , in which a fiber cross section shape is not a round shape but a flat shape such as an elliptical shape , oblong - circular shape , rectangle shape , a shape in which half rounds are connected to both short sides of a rectangle , and cocoon shape . a converted fiber diameter and a fiber length of the flat glass fibers used in the present invention are not particularly limited . a converted fiber diameter is preferably from 3 μm to 30 μm , further preferably from 5 μm to 20 μm . when it is less than 3 μm , it may be difficult to produce a glass fiber . when it exceeds 30 μm , an effect of strength properties may not be obtained . a fiber length of the flat glass fibers contained in the resulting foam - molded article is preferably from 50 μm to 10000 μm , further preferably from 100 μm to 1000 μm . in the meantime , a converted fiber diameter of the flat glass fibers represents a number average fiber diameter measured when the flat cross section shape is converted to a complete round shape having an area same as an area of the flat cross section shape ( a converted fiber diameter which represents a diameter of a round shape having an area same as an area of a cross section shape of said flat glass fibers ). in the meantime , a converted fiber diameter is obtained by measuring a weight per unit length of filaments of the flat glass fibers with a precision balance , dividing the weight by a specific gravity of a glass to determine a cross section area , and calculating a diameter of a corresponding complete round shape having the cross section area to determine the converted fiber diameter . the converted fiber diameter d can be also specifically determined by the following calculation formula : tex : yarn number of flat glass fibers ( grams per 1000 m ) an aspect ratio (= major axis / minor axis ) of a fiber cross section of the flat glass fibers is preferably from 1 . 5 to 10 , further preferably from 2 . 0 to 6 . 0 . when the aspect ratio is less than 1 . 5 , the molded article may not have a sufficient impact resistance or heat resistance . when the aspect ratio exceeds 10 , it may be difficult to product a glass fiber per se . the aspect ratio described at the present specification can be determined from an observed image obtained by observing a cross section of the glass fiber with a scanning electron microscope ( sem ). that is , the aspect ratio is obtained by calculating a (= a length of ra )/ b (= a length of rb ) based on lengths of a and b determined from a long side ra and a short side rb of a rectangle circumscribed to the flat glass fiber in the observed image as shown in fig1 . kinds of glasses used for the flat glass fibers in the present invention can include a glass having a general glass fiber composition such as e glass , and any compositions for a possible glass fiber such as t glass , ne glass , c glass , s glass , s2 glass and r glass , and are not particularly limited . the flat glass fibers can be produced by a production method of a known glass fiber , and can be used as an embodiment of a chopped strand prepared by cutting , in a constant length , a collected glass fiber strand focused by a known sizing agent suitable for a blending resin containing an antistatic agent and a film forming agent etc . in addition to a silane coupling agent such as a silane coupling agent , a titanium type coupling agent and a zirconia type coupling agent for an enhancement of a uniform dispersibility and an adhesiveness with a matrix resin , or can be used as an embodiment of a long fiber - reinforced thermoplastic resin pellet coated with a resin . a content of the flat glass fibers in a resin composition in the flat glass fiber - reinforced polyamide resin foam - molded article of the present invention can be about from 1 to 40 wt %, preferably from 3 to 30 wt %, more preferably from 5 to 15 wt %. when the content of the flat glass fibers is less than 1 wt %, a reinforcement effect may not be sufficiently obtained . when the content of the flat glass fibers exceeds 40 wt %, an appearance of a molded article may be deteriorated or a weight saving may become difficult . the resin used in the present invention can include a thermoplastic resin and a thermosetting resin . the thermoplastic resin can include a general - purpose resin and an engineering plastic . the general - purpose resin can include polyethylene , polypropylene , polyvinyl chloride , polystyrene and abs resin and the like , but is not limited thereto . the engineering plastic can include a general - purpose engineering plastic and a specialty engineering plastic . the general - purpose engineering plastic can include polyamide , polyacetal , polyester , polycarbonate , and modified polyphenylene ether and the like , but is not limited thereto . the specialty engineering plastic can include polysulfone , polyarylate , polyetherimide , polyamide imide , polyphenylene sulfide and liquid crystalline polyester and the like , but is not limited thereto . the thermosetting resin can include a phenol resin , a urea resin , a melamine resin , an unsaturated polyester resin , an epoxy resin , polyurethane and a silicone resin and the like , but is not limited thereto . of these resins , a polyamide resin is preferred . the polyamide resin represents a polyamide resin mainly composed of amino acid , lactam or dicarboxylic acid and diamine , but the usable polyamide resin is not particularly limited . for example , it can include polycaproamide ( nylon 6 ), polyhexamethylene adipamide ( nylon 66 ), polytertamethylene adipamide ( nylon 46 ), polyhexamethylene sebacamide ( nylon 610 ), polyhexamethylene dodecamide ( nylon 612 ), polyhexamethylene adipamide / polyhexamethylene terephthal amide copolymer ( nylon 66 / 6t ), polyhexamethylene adipamide / polyhexamethylene isophthal amide copolymer ( nylon 66 / 6i ), polycaproamide / polyhexamethylene adipamide / polyhexamethylene isophthal amide copolymer ( nylon 6 / 66 / 6i ), polyhexamethylene adipamide / polyhexamethylene terephthal amide / polyhexamethylene isophthal amide copolymer ( nylon 66 / 6t / 6i ), polyxylylene adipamide ( nylon xd6 ), polynonamethylene terephthal amide ( nylon 9t ), polynonamethylene isophthal amide ( nylon 9i ), polynonamethylene terephthal amide / polynonamethylene isophthal amide ( nylon 9t / 9i ), polyxylylene diamine adipamide ( nylon mxd6 ), nylon 12 , nylon 11 , and a mixture or copolymer thereof . in the meantime , t represents a terephthalic acid unit , and i represents an isophthalic acid unit . for the purpose of enhancing properties of a heat resistance , a chemical resistance , an abrasion resistance and a mechanical strength of these polyamide resins , a mixture of two or more kinds of polyamide resins can be practically and suitably used . preferred one is one or more kind selected from nylon4 , nylon 6 , nylon 11 , nylon 66 , nylon 6t , nylon mxd6 and nylon 9t , and a particularly preferred one is nylon 6 and nylon 9t . in the present invention , the resin can be used e . g . in the form of pellet or powder , but is not limited to thereto . additionally , insofar as the purpose of the present invention is not deteriorated , it is possible to add , to a main constitutional component resin ( preferably a polyamide resin ), another resin ( preferably a polyamide resin ) or other polymers , an additive , a crystal nucleating agent , a stabilizer such as a heat resistant agent and a uv light absorber , a flame retardant , an antistatic agent , a plasticizer , a lubricant , a coloring agent or a coupling agent and the like , according to properties required . a means used for mixing the resin with flat glass fibers can include a known technology , and can include a method of melt - kneading with a single screw extruder or a twin screw extruder , but is not particularly limited thereto . from the viewpoint of obtaining a good kneading state , it is preferred to use a twin screw extruder . it is preferred that a kneading temperature is from ( a melting point of the resin + 5 ° c .) to ( a melting point of the resin + 100 ° c .) and a kneading period of time is from 20 seconds to 30 minutes . in case of a lower temperature or a shorter period of time than these ranges , a kneading or reaction may be insufficient . in contrast , in case of a higher temperature or a longer period of time than these ranges , a decomposition or coloring of the resin may occur . thus , both cases are not preferable . in order to secure a form stability , it is preferred that raw materials other than a glass fiber are sufficiently melt - kneaded and then a prescribed amount of flat glass fibers is side - fed and subject to a vacuum deaeration . the flat glass fiber - reinforced resin composition used in the present invention can optionally contain an inorganic filler . an improvement of surface properties etc . of a molded article can be further attempted by using , as the inorganic filler , several kinds of fibrous or non - fibrous inorganic fillers generally used for a reinforced resin . examples of the inorganic filler can include e . g . : a fibrous filler such as a glass fiber ( having a round shape cross section ), a carbon fiber , a potassium titanate whisker , a zinc oxide whisker , an aluminum borate whisker , an aramid fiber , an alumina fiber , a silicon carbide fiber , a ceramic fiber , an asbestos fiber , a gypsum fiber and a metal fiber ; a silicate such as wollastonite , zeolite , sericite , kaolin , mica , clay , pyrophilite , bentonite , asbestos , talc and alumina silcate ; a metallic oxide such as alumina , silicon oxide , magnesia oxide , zirconium oxide , titanium oxide and iron oxide ; a carbonate such as calcium carbonate , magnesium carbonate and dolomite ; a sulfate such as calcium sulfate and barium sulfate ; a hydroxide such as magnesium hydroxide , calcium hydroxide and aluminum hydroxide ; and a non - fibrous filler such as a glass flake , a glass bead , a ceramic bead , boron nitride , silicon carbide and silica , which can be hollow . plural kinds of these inorganic filler can be used together . additionally , from the viewpoint of obtaining better mechanical properties or appearance of a molded article , it is preferred to use these fibrous or non - fibrous inorganic fillers by being simultaneously or after being preliminarily treated with a coupling agent such as an isocyanate type compound , an organosilane type compound , an organotitanate type compound , an organoborane type compound and an epoxy compound . the foaming agent used in the present invention can include a chemical foaming agent and a physical foaming agent , but is not limited thereto . the chemical foaming agent can include an inorganic type foaming agent and an organic type foaming agent . the inorganic foaming agent can include sodium bicarbonate , ammonium bicarbonate , ammonium carbonate , ammonium nitrite , ammonium borohydride , an azide compound , a light metal and the like , but is not limited thereto . the organic foaming agent can include an azo compound , a nitroso compound , a sulfonyl hydrazide compound , a sulfonyl semicarbazide compound and the like , but is not limited thereto . the physical foaming agent can include : an inorganic type foaming agent such as carbon dioxide , nitrogen , argon , helium and air ; and an organic type foaming agent such as pentane , butane , hexane , methyl chloride , methylene chloride , fluorinated aliphatic hydrocarbon ( e . g . trichlorofluoromethane ), but is not limited thereto . of them , the foaming agent used in the present invention is preferably a supercritical fluid , particularly a gas at a supercritical state . the gas at a supercritical state , which is preferably used in the present invention and becomes an air bubble nucleus , can include carbon dioxide , nitrogen , argon , helium and the like , but is not limited thereto . additionally , it can be used alone or as a mixture of two or more kinds thereof . of these gases , from the viewpoint of a stability and a permeability into a polyamide resin , carbon dioxide and nitrogen are particularly preferred . an amount of the foaming agent ( a supercritical fluid ) to be charged at the time of injection foam molding of the resin is not particularly limited , but is preferably from 0 . 001 to 5 . 0 parts by weight , more preferably from 0 . 002 to 3 . 0 parts by weight , further preferably from 0 . 005 to 1 . 0 part by weight , relative to 100 parts by weight of the resin . when the amount of the foaming agent ( a supercritical fluid ) is less than 0 . 001 part by weight , a gas injection device has a tendency not to be stably worked . when it exceeds 5 . 0 parts by weight , a foaming of an injected product has a tendency not to be stable because an amount of gas is excess . a method of injecting a supercritical fluid to a flat glass fiber - reinforced resin at a molten state at the injection foam molding is not particularly limited , but can include e . g . a method of injecting a gas at a gas state as it is , a method of injecting under pressure , a method of injecting under vacuum , and a method of a gas at a liquid state or a supercritical fluid state with a ram pump etc ., and the like . next , one example of a method for producing the flat glass fiber - reinforced resin foam - molded article of the present invention is explained below by referring to the schematic diagram of fig3 . first , a flat glass fiber - reinforced polyamide resin pellet a , as a molding material , is fed from a hopper b of an extruder , and is heat - molten . an inert gas such as nitrogen and carbon dioxide , which becomes a supercritical fluid , is fed from a gas cylinder k , is boosted with a booster pump j , and then is fed to a molten flat glass fiber - reinforced polyamide resin in a cylinder d . during them , an inside of the cylinder d keeps the fed inert gas at a supercritical state and keeps a critical temperature or more and a critical pressure or more so as to dissolve / diffuse into the molten flat glass fiber - reinforced polyamide resin in a short period of time . for example , in case of nitrogen , a critical temperature is − 127 ° c . and a critical pressure is 3 . 5 mpa ; and , in case of carbon dioxide , a critical temperature is 31 ° c . and a critical pressure is 7 . 4 mpa . the molten flat glass fiber - reinforced polyamide resin and the inert gas are kneaded with a screw c in the cylinder d , and further a complete compatibility state of the molten flat glass fiber - reinforced polyamide resin and the inert gas is formed by a static mixer e and a diffusion chamber f , and then it is injected into a cavity h of a mold i and a pressure is released to form a fine foam - molded article . at this moment , it is possible to control a foaming diameter by loading a counter pressure in the mold i , and , if required , an inert gas can be fed from a gas cylinder l . a pressure at the time thereof is not particularly limited , but is preferably from 0 . 5 to 15 mpa . a method of promoting a foaming by rapidly lowering a pressure in the mold can include a method of injecting the molten flat glass fiber - reinforced polyamide resin into the cavity h of the mold i and then rapidly increasing an inner volume inside of the mold by allowing a part or whole of a core of the mold to pull back . the flat glass fiber - reinforced resin foam - molded article of the present invention can be applied to all uses which a glass fiber - reinforced resin can be generally applied to . for example , an automobile field requiring a large weight saving can include a cylinder head cover , a timing - belt cover , a balance shaft gear , and the like . additionally , uses other than an automobile can include not only a personal computer , a liquid crystal projector , a mobile device , a case of a cellular phone etc ., an internal combustion engine use , a machine component for power tool housings etc ., but also several kinds of electrical and electronics parts , a medical equipment , a food container , a household good , a stationery , a building material part and a furniture part etc . in the meantime , an example of a molding in the molding method and the molded article of the present invention mentions an injection above , but is not limited to an injection and can be applied to other moldings such as a compression molding , a transfer molding , an extrusion molding , a blow molding , a cast molding , a vacuum processing , a pressure processing , a calcination processing , bmc ( bulk molding compound ), smc ( sheet molding compound ) and a sheet stamping etc . examples are shown below , and the present invention is further specifically explained by the examples , but the present invention is not limited to the following examples . injection foaming conditions and test conditions are as follows . a constitutional sketch of the injection molding machine is show at fig3 . temperatures of the cylinder d from a hopper b side toward a nozzle g side were set up to as follows . carbon dioxide was used . an amount thereof injected was 0 . 01 g relative to 100 g of the glass fiber - reinforced polyamide resin . it was 90 ° c . in case of nylon 6 . it was 120 ° c . in case of nylon 9t . ( 1 ) flat glass fiber ( flat glass fiber commercially available from nitto boseki co ., ltd . : # 820 ): a strand bundling the glass fibers having a kind of glass of e glass , an aspect ratio of 4 , a converted fiber diameter of 11 μm , and a cross section shape of an oblong - circular shape . ( 2 ) round glass fiber ( glass fiber commercially available from nitto boseki co ., ltd . : # 451 ): a strand bundling the glass fibers having a kind of glass of e glass and a glass fiber diameter of 11 μm . ( 3 ) flat glass fiber ( flat glass fiber commercially available from nitto boseki co ., ltd . : # 820 ): a strand bundling the glass fibers having a kind of glass of e glass , an aspect ratio of 4 , a converted fiber diameter of 15 μm , and a cross section shape of an oblong - circular shape was cut in 3 mm length each to form a chopped strand which was used . ( 1 ) nylon 6 resin ( commercially available from ube industries , ltd .) ( 2 ) nylon 9t resin ( commercially available from kuraray co ., ltd .). as test specimens for evaluations , jis ( japanese industrial standard ) number 1 type tensile test specimen and a flat plate having a size of 50 mm × 195 mm × 1 . 5 mm were foam - injection molded . tensile properties for the former test specimen were evaluated , and evaluations of a warpage , a sink mark and a surface impact strength for the latter test specimen were conducted . 1 ) tensile strength : tensile strength was measured according to jis k7113 . 2 ) warpage and sink mark : warpage and sink mark of the resulting foam - molded article were evaluated according to visual observation . 3 ) weight saving coefficient : weight saving coefficient was calculated according to the following expression . [ weight saving coefficient ](%)=[ weight of foam - molded article ]/[ weight of usual injection molded article ( without foam molding )]× 100 4 ) surface impact properties : after an iron plummet having a weight of 500 g was dropped from a height of 500 mm down on a center section of the test specimen of a glass fiber - reinforced polyamide resin molded article in the flat plate form having a size of 50 mm × 195 mm × 1 . 5 mm , surface impact properties were evaluated by observing a state of the molded article according to visual observation . nylon 6 resin ( pa6 resin ) incorporating flat glass fibers having a converted fiber diameter of 15 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a supercritical foam molding by using carbon dioxide ( co 2 ) as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 1 . nylon 6 resin incorporating flat glass fibers having a converted fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a supercritical foam molding by using carbon dioxide ( co 2 ) as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 1 . nylon 9t resin ( pa9t resin ) incorporating flat glass fibers having a converted fiber diameter of 15 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a supercritical foam molding by using carbon dioxide ( co 2 ) as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 1 . nylon 9t resin incorporating flat glass fibers having a converted fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a supercritical foam molding by using carbon dioxide ( co 2 ) as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 1 . nylon 6 resin incorporating round glass fibers having a fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a supercritical foam molding by using carbon dioxide ( co 2 ) as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . additionally , fig2 shows photomicrographs of a surface state of the molded article after conducting a drop impact strength test by using the resulting molded article in the form of flat plate . nylon 9t resin incorporating round glass fibers having a fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a supercritical foam molding by using carbon dioxide ( co 2 ) as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . nylon 6 resin incorporating round glass fibers having a fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a usual injection molding without using as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . nylon 6 resin incorporating flat glass fibers having a converted fiber diameter of 15 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a usual injection molding without using as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . nylon 6 resin incorporating flat glass fibers having a converted fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a usual injection molding without using as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . nylon 9t resin incorporating round glass fibers having a fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a usual injection molding without using as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . nylon 9t resin incorporating flat glass fibers having a converted fiber diameter of 15 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a usual injection molding without using as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . nylon 9t resin incorporating flat glass fibers having a converted fiber diameter of 11 μm in an amount of 10 wt % relative to the resin was melt - kneaded to form a material , and the material was subjected to a usual injection molding without using as a supercritical fluid . evaluation results of physical properties and appearances of the resulting molded article are shown at table 2 . in the meantime , in respect to the results of the surface impact test of the flat plate in example 1 , example 2 and comparative example 1 , fig2 shows photographs which were taken in operating the surface impact test and which were taken from a side and just below of a molded article in the form of flat plate after dropping an iron plummet . 1 ) according to the results of examples 1 and 2 and comparative example 1 , it is clearly understood that , in case of using a pa6 resin , a supercritical foam - molded article obtained by using flat glass fibers results in a molded article having better physical properties and a molded article in the form of box having no warpages or sink marks than a foam - molded article obtained by using round glass fibers . additionally , it is understood according to the results of fig2 that also surface impact properties in the molded article obtained by using flat glass fibers are better than in the molded article obtained by using round glass fibers . 2 ) particularly , according to a comparison of example 2 using flat glass fibers having a converted fiber diameter of 11 μm to comparative example 1 using round glass fibers having an identical fiber diameter of 11 μm , a tensile strength is 49 mpa in round glass fibers while it is 81 mpa in flat glass fibers , which means that an improvement ratio by using flat glass fibers relative to the case of using round glass fibers is 65 . 3 % increase which is remarkable enhancement . it is understood that the value of 81 mpa in flat glass fibers ( example 2 ) is almost equivalent to 86 mpa in a usual injection molded article , but not a foam - molded article , obtained by using flat glass fibers ( referential example 3 ). for reference &# 39 ; sake , in case of not a foam - molded article in referential examples , tensile strengths are 86 mpa and 67 mpa in usual injection molded articles obtained by using flat glass fibers ( referential example 3 ) and by using round glass fibers ( referential example 1 ), respectively . it means that an improvement ratio by using flat glass fibers relative to the case of using round glass fibers is just 28 . 4 % increase . in view thereof , the above 65 . 3 % increase , which is an improvement ratio by using flat glass fibers in the foam - molded article relative to the case of using round glass fibers , is much beyond an expectation and is remarkable enhancement . in a supercritical injection foam molding , a strength decreasing rate due to a preparation of a foam - molded article as compared to a usual injection molding is 26 . 9 % in round glass fibers while it is 5 . 8 % in flat glass fibers , and it is clear that the strength decreasing in flat glass fibers is very small . these situations are summarized at table 3 . 3 ) the case of using pa9t resin is almost similar , and , according to the results of examples 3 and 4 and comparative example 2 , also the pa9t resin obtains a molded article having good physical properties and a molded article having no warpages or sink marks as well as the pa6 resin . particularly , according to a comparison of example 4 using flat glass fibers having a converted fiber diameter of 11 μm to comparative example 2 using round glass fibers having an identical fiber diameter of 11 μm , a tensile strength is 23 mpa in round glass fibers while it is 43 mpa in flat glass fibers , which means that an improvement ratio by using flat glass fibers relative to the case of using round glass fibers is 87 . 0 % increase which is remarkable enhancement . tensile strengths are 60 mpa and 50 mpa in usual injection molded articles ( not foam - molded articles ) obtained by using flat glass fibers ( referential example 6 ) and by using round glass fibers ( referential example 5 ), respectively . it means that an improvement ratio by using flat glass fibers relative to the case of using round glass fibers is just 20 % increase . in view thereof , the above 87 . 0 % increase , which is an improvement ratio by using flat glass fibers in the foam - molded article relative to the case of using round glass fibers , is remarkable enhancement . these situations are summarized at table 4 . additionally , according to table 4 , in a supercritical injection foam molding , a strength decreasing rate due to a preparation of a foam - molded article as compared to a usual injection molding is 54 . 0 % in round glass fibers while it is 28 . 3 % in flat glass fibers , and it is clear that the strength decreasing in flat glass fibers is very small . as mentioned above , the injection foam - molded article of the present invention prepared from a reinforced resin ( particularly a polyamide resin ) by using a foaming agent ( particularly a supercritical fluid ) can retain good physical properties such as small sink marks or warpages , which properties were not able to be obtained in a conventional injection foam - molded article , and can secure a good mechanical strength due to the use of the flat glass fibers , and thus it is understood that a weight saving can be sufficiently accomplished . additionally , an impact resistance is also enhanced , and thus it is understood that it is suitably used for several kinds of applications including a mobile application . in the meantime , an injection molding method by using a gas at a supercritical state is mentioned as an injection molding method in the above examples , but similar matters can be expected also in other molding methods such as an extrusion molding method .