hereinafter , a preferred embodiment of the present invention will be described with reference to the accompanying drawings . in the following description and drawings , the same reference numerals are used to designate the same or similar components , and so repetition of the description on the same or similar components will be omitted . fig3 shows a perspective view of a sewing machine according to the present invention . referring to the drawing , a head portion 40 is positioned above a table 10 . the head portion 40 performs a sewing operation on a material retained on a retainer 50 . the table 10 is a square plate on which the material to be sewn is placed . the table 10 is provided with guide holes 12 elongated in the forward and backward director along its opposite sides . the guide holes 12 are adapted to transmit the movement of a y - axis feeding means 70 ( fig4 ), positioned below the table 10 , to a retainer 50 , positioned above the table 10 . supporting posts 22 are formed vertically on the opposite ends of the table 10 . a holding frame 20 is supported between the supporting posts 22 in the horizontal direction . the holding frame 20 is preferably made of a rectangular steel tube and has a head portion 40 extending forward from its center portion . an arm lifting device 30 is preferably provided between the head portion 40 and the holding frame 20 to move the head portion 40 upward or downward . the sewing machine according to the present invention makes it possible to sew a material in an extended area while the head portion 40 is held , because the retainer 50 is adapted to move in the x - axis and y - axis direction . for this , the holding frame 20 is positioned horizontally for openness in the forward and backward direction , opposite ends of which being supported by the supporting post 22 , so that the head portion 40 is held in a bridge - like fashion . fig3 to 5 show an arrangement for moving the retainer 50 in the x - axis or y - axis direction . an upper shaft driving motor 39 is provided behind the holding frame 20 to drive an upper shaft ( not shown ) within the head portion 40 . the upper shaft driving motor 39 is connected to the upper shaft ( not shown ), but not to a lower shaft ( not shown ) for driving a shuttle race body ( not shown ). fig4 shows a front view of a sewing machine according to the present invention . referring to the drawing , an x - axis feeding means 60 is provided above the table 10 and extends in the x - axis direction . multiple y - axis feeding means 70 are provided below the table 10 and extend in the y - axis direction . the x - axis feeding means 60 comprises an x - axis frame 62 elongated in the x - axis direction , a guide rail 64 installed or formed on the x - axis frame 62 , and a holding portion 66 adapted to move leftward or rightward in accordance with the guide rail 64 . the retainer 50 , on which a material to be sewn is retained , is coupled to the holding portion 66 . as the holding portion 66 can move leftward or rightward , it is possible to sew a material in an extended area in the x - axis direction without any movement of the head portion 40 . the y - axis feeding means 70 enable movement of the retainer 50 in the y - axis direction , that is , in the forward or backward direction . the y - axis feeding means 70 extend in the forward and backward direction and have moving portions 72 adapted to move in the forward or backward direction . the moving portions 72 are preferably made of belts 72 a adapted to move in the forward or backward direction . holders 72 b are coupled on top of the belt 72 a and protrude upward . the holders 72 b are displaced forward or backward in accordance with the movement of the belts 72 a . each of the y - axis feeding means 70 , positioned on opposite sides of the table 10 , is provided with its own holder 72 b in parallel orientation . the guide holes 12 of the table 10 expose the holders 72 b upward . the x - axis frame 62 is connected to the holders 72 b . when the x - axis feeding means 60 is not coupled , direct connection could be possible using additional extensions from the retainer 50 in the leftward and rightward direction . as the holders 72 b move forward or backward in accordance with the movement of the moving portions 72 — i . e . the belts 72 a — the retainer 60 , which is connected to the x - axis frame 62 , is displace forward or backward accordingly . this makes it possible to sew a material in an extended area in the y - axis direction without any movement of the head portion 40 . a lower shaft driving motor 39 is positioned below the table 10 to transmit power to a lower shaft ( not shown ), which is adapted to drive a shuttle race body ( not shown ). according to the inventive sewing machine , the upper and lower shafts should each be driven separately because , unlike in the prior art , the head portion 40 is held in a bridge - like fashion . more specifically , a prior sewing machine has a body 203 ( fig1 and 2 ) positioned in its center portion and a single driving motor 230 for driving the upper and lower shafts 210 and 220 simultaneously . however , the inventive sewing machine has an additional lower shaft driving motor 89 for separate driving of the shafts . a control unit ( not shown ) controls the driving operation of the upper and lower shafts 38 and 39 . fig5 shows a side elevation view of a sewing machine according to the present invention . referring to the drawing , each of the x - axis feeding means 60 has an x - axis feeding motor 68 and the y - axis feeding means 70 extend in the forward and backward direction along the side . the x - axis feeding means 60 is positioned above the table 10 and is connected to the retainer 50 . the y - axis feeding means 70 is positioned below the table 10 and is connected to the x - axis feeding means 60 through the guide hole 12 . reference numeral 42 denotes a needle . fig6 shows a top view illustrating an x - axis feeding means and y - axis feeding means according to the present invention . referring to the drawing , the x - axis feeding means 60 has an x - axis driving motor 68 provided on a side thereof for driving movement in the leftward or rightward direction the y - axis feeding means 70 have a y - axis driving motor 74 for driving movement in the forward or backward direction . the x - axis driving motor 68 rotates a driving pulley 68 b coupled to a driving shaft 68 a which faces forward . this rotation moves a belt 69 leftward or rightward , which is wound around the driving pulley 68 b . as the belt 69 is moved , a holding portion 66 connected thereto is moved accordingly . as a result , the retainer 50 , which is coupled to the holding portion 66 , is displaced a following pulley ( not shown ), which is provided on an end opposite from the end on which the driving pulley 68 b is provided , winds the belt 69 . the y - axis driving motor 74 is connected , via driving shafts 74 a , to the rear portions of the y - axis feeding means 70 , which extend in the forward and backward direction along opposite sides of the table . as the y - axis driving motor 74 is rotated , the belts 72 a which are wound around driving pulleys ( not shown ) are moved forward or backward accordingly . holders 72 b are coupled on top of the belts 72 a and protrude upward . the holders 72 b move the x - axis feeding means 60 horizontally forward or backward in accordance with the movement of the belts 72 a . the belts 72 a are wound around driving pulleys ( not shown ) at their rear portions , as well as around following pulleys ( not shown ) at their front portions . fig7 shows an exploded perspective view of an arm lifting device according to the present invention . referring to the drawing , a guide plate 32 , which is fixedly coupled to the holding frame 20 , engages a feeder 34 , which is fixedly coupled to the head portion 40 , within the arm lifting device 30 . the guide plate 32 is in the shape of a bar elongated in the upward and downward direction and is hollow in its center portion , as in the case of a rail used in the railway . the feeder 34 has rear ends defining a narrowed space between them so that the guide plate 32 can be fitted from above or below into the space . the hollow portion of the guide plate 32 is fitted with the rear ends of the feeder 34 . as a result , the feeder 34 can slide upward or downward relative to the guide plate 32 , but cannot move laterally , i . e ., in the forward or backward directions . movement of the arm lifting device 30 in the upward or downward direction can be realized , for example , by means of a pneumatic or hydraulic cylinder or via a mechanical structure , such as the rotation of a screw structure , but the means for movement is not limited thereby . more specifically , the arm lifting device 30 is supported by the holding frame 20 and the head portion 40 is connected to the arm lifting device 30 . a control box ( not shown ) controls the upward and downward movement through a structure using a pneumatic or hydraulic cylinder or a mechanical structure using a screw . fig8 a and 8 b show side sectional views illustrating a head portion lowered and lifted respectively by an arm lifting device according to the present invention . referring to the drawing , the feeder 34 , which is integrated and moved together with the head portion 40 , is displaced upward or downward in accordance with the guide plate 32 , which is integrated to the holding frame 20 . when the arm lifting device 30 applies pneumatic pressure through an upper pneumatic pressure opening ( not shown ), the lifting plate 36 within the arm lifting device 30 is pushed down from above and lowered accordingly . this makes the feeder 34 descend along the guide plate 32 and , as a result , the head portion 40 is moved downward . when the head portion 40 is to be moved upward , on the other hand , pneumatic pressure is discharged through a lower pneumatic pressure opening ( not shown ). the lifting plate 36 within the arm lifting device 30 is then lifted . this makes the feeder 34 ascend along the guide plate 32 and , as a result , the head portion 40 is moved upward . if the head portion 40 has finished its operation , the arm lifting device 30 lifts the head portion 40 to facilitate removal of the sewn material . if another material is placed in position to be sewn , the head portion 40 is lowered for sewing so that the needle 42 can approach the material . this behavior makes it possible to use the retainer 50 in the sewing machine more efficiently and to sew thicker materials , although only materials the thicknesses of which are below a determined value can be sewn with prior sewing machines . the present invention eliminates any coupling portion between an arm and a bed , as used in prior sewing machines . instead , the inventive sewing machine has a holding frame supported by support posts , a head portion mounted on the holding frame , and a means for driving its upper shaft separately . due to an arch - shaped arrangement positioned on its center portion without any structure for connecting upper and lower portions , sewing area is substantially increased in the y - axis direction . accordingly , it is possible to sew materials with unlimited length , such as a long cloth , without any interruption . in addition , the retainer can be lifted when sewing is started or finished and the head portion can be moved up and down . this makes it possible to easily place and remove the material to be sewn and to process materials with various thicknesses , although only thin materials can be sewn with conventional sewing machines . the inventive sewing machine separately drives its upper and lower shafts using separate driving motors . this avoids any overloading to single motor adapted to drive upper and lower shafts simultaneously via , for example , a timing belt . although a preferred embodiment of the present invention has been described for illustrative purposes , those skilled in the art will appreciate that various modifications , additions and substitutions are possible , without departing from the scope and spirit of the invention as disclosed in the accompanying claims .