several embodiments of the present invention will be described . fig1 to 5 b illustrate a first embodiment in accordance with the invention . referring to fig1 , an overall construction of a drum type washer - drier of the first embodiment is shown . the drum type washer - drier includes a base 1 made of a resin . a generally rectangular outer cabinet 2 is mounted on the base 1 . the cabinet 2 includes a front cover 3 having a centrally formed access opening 3 a ( see fig2 ) through which laundry is put into and taken out of a drum . a door 4 is mounted on the front cover 3 so as to open and close the opening 3 a . an operation panel 5 is mounted on the front cover 3 so as to be located above the door 4 . the operation panel 5 is provided with various switches for selecting or setting an operation course or the like . a wash operation , a dehydration operation or a wash - dehydration operation in which the wash and dehydration operations are continuously carried out can be selected on the operation panel . referring now to fig2 , a cylindrical water tub 6 is supported by suspension mechanisms 7 ( only one shown ) which are further mounted on the base 1 . each suspension mechanism 7 includes a coil spring and a damper . thus , the water tub 6 is mounted on the base 1 in the cabinet 2 . a drum 8 made of stainless steel ( sus403 , for example ) is mounted in the water tub 6 . the water tub 6 and the drum 8 serve as a wash tub in combination . each of the water tub 6 and the drum 8 is disposed so that a central axis thereof is inclined rearwardly downward . a brushless dc motor 9 of the outer rotor type is fixed to a rear end of the water tub 6 . the motor 9 includes a shaft 10 which extends through an end face of the water tub 6 into an interior of the water tub 6 . the shaft 10 has a distal end connected to a drum support 11 mounted on an end plate 8 b of the drum 8 . upon rotation of a rotor of the motor 9 , the shaft 10 is rotated together with the rotor , whereby the drum 8 is rotated . the drum 8 includes a peripheral wall and the end plate 8 b both formed with a number of holes 12 serving both as air vents and as water vents . some of the holes 12 are shown in fig2 . furthermore , a drain hole ( not shown ) is formed through the lower rear ( lowermost portion ) of the water tub 6 . a drain pipe 13 is connected to the drain hole . a lower end of the drain pipe 13 is connected via a drain valve 14 to another drain pipe 15 . the water tub 6 and drum 8 have front ends formed with openings 6 a and 8 a respectively . the openings 6 a and 8 a communicate via bellows 16 with the opening 3 a of the front cover 3 . a ventilation duct 17 is provided over the top of the water tub 6 so as to face the interior of the water tub . the ventilation duct 17 is provided with a heater 18 . a blowing fan 19 is provided at an upstream side with respect to the ventilation duct 17 . the blowing fan 19 supplies air flow into the water tub 6 . a further upstream side of the ventilation duct 17 is connected to the water tub 6 so as to face the interior of the water tub . furthermore , a heat pump including a condenser and an evaporator is also provided though not shown . accordingly , upon operation of the heater 18 and blowing fan 19 , air in the water tub 6 and drum 8 is adapted to be circulated and dehumidified upon operation of the heater 18 and blowing fan 19 . additionally , a control device 20 is provided inside the operation panel in the interior of the cabinet 2 . the control device 20 controls an overall operation of the washer - drier . a user operates switches on the operation panel 5 so that an operation course is set in the washer - drier constructed as described above . when start of operation is instructed , a washing operation or a drying operation is carried out according to a set operation course or a washing - drying operation is carried out so that washing and drying operations are continuously carried out . for example , when the washing - drying operation has been started , a wash step , a dehydration step and a drying step are sequentially carried out . a concrete construction of the mounting portion of the drum support 11 on the drum 8 will now be described with reference to fig3 and 4 . fig3 shows the drum support 11 mounted on the drum 8 . the drum support 11 includes a central portion 11 a and three protrusions 11 b extending radially from the central portion 11 a at regular intervals . the drum support 11 is die - cast from aluminum . the drum support 11 has an outer surface or a side opposite the end plate 8 b of the drum 8 . a number of ribs 11 c protrude from the outer surface of the drum support 11 configured as shown in fig3 . the ribs 11 c constitute a reinforcing corrugated portion of the drum support 11 . the end plate 8 b of the drum 8 has a recess 8 c in which the drum support 11 is to be accommodated . the recess 8 c is formed so as to be swollen inside the drum 8 . in this case , the drum support 11 is accommodated in the recess 8 c and thereafter , distal ends of the respective protrusions 11 b of the drum support 11 are screwed onto the peripheral wall of the drum 8 . furthermore , the drum support 11 is fixed to the drum 8 by scrimping . referring now to fig4 , a rectifying cover 21 is mounted on the end plate 8 b of the drum 8 so as to close the recess 8 c and so as to cover the drum support 11 . the rectifying cover 21 is made of stainless steel ( sus403 ) which is the same material as the drum 8 . the rectifying cover 21 is formed so as to be larger than the recess 8 c . the rectifying cover 21 has a centrally located through hole 21 a through which the shaft 10 and the like are to be inserted ( see fig3 ). the end plate 8 b of the drum 8 and the rectifying cover 21 are adapted to be substantially co - planar when the rectifying cover 21 is mounted on the end plate 8 b . the rectifying cover 21 is screwed on the end plate 8 b by making using of some of the holes 12 formed through the end plate . the drum support 11 is accommodated in the recess 8 c of the drum 8 to be fixed therein . the recess 8 c is then mounted on the end plate 8 b so as to close the recess 8 c and cover the drum support 11 . as a result , since an outer surface of the end plate 8 b is substantially flat , rotational resistance and accordingly noise can be reduced when the drum 8 is rotated at high speeds ( 1400 rpm , for example ) in the dehydration step . furthermore , power consumption of the washer - drier can also be reduced as the result of reduction in the rotational resistance . fig5 a and 5b show the results of measurement of noise regarding the washer - drier of the embodiment . more specifically , fig5 a and 5b show the results of fast fourier transform ( fft ) analysis carried out with respect to noise produced from dehydration operation of the drum type washer - drier of the embodiment . fig5 a shows the results of measurement with respect to the construction before attachment of the rectifying cover 21 , whereas fig5 b shows the results of measurement with respect to the construction after attachment of the rectifying cover 21 . the axis of abscissas represents frequency in hz and the axis of ordinates represents sound pressure level in db in fig5 a and 5b . in comparison of fig5 a and 5b , it can be considered that the sound pressure level is sufficiently reduced in a frequency band ranging from about 2 khz to about 5 khz when the rectifying cover 21 is attached to the drum 8 . it is noted that the aforesaid frequency band corresponds to the noise produced by the frequency band ( the frequency band of not more than about 2 khz corresponds to noise produced by the motor ). furthermore , since the rectifying cover 21 and the drum 8 are made of the same material , that is , stainless steel ( sus403 ), crevice corrosion can be restrained in the washer - drier of the embodiment as compared with the construction in which the rectifying cover and the drum are made of different materials . additionally , the drum support 11 includes the central portion 11 a and the three protrusions 11 b extending radially from the central portion 11 a at regular intervals . since the rectifying cover is formed so as to correspond to the shape of the drum support 11 , an amount of material for the rectifying cover 21 can be reduced in the embodiment as compared with the case where an entire end plate 8 b is covered with a rectifying cover . fig6 illustrates a second embodiment of the invention . in the second embodiment , similar or identical parts are labeled by the same reference symbols as those in the first embodiment . as shown in fig6 , the rectifying cover 22 in the second embodiment is sized so that portions of the outer periphery of the recess 8 are exposed . more specifically , the rectifying cover 22 is formed so that a radial dimension thereof is slightly shorter that that of the end plate 8 b . when the rectifying cover 22 is mounted on the end plate 8 b , gaps 8 e are defined between the outer periphery of the recess 8 c and the rectifying cover 22 . the other construction of the washer - drier of the second embodiment is substantially the same as in the first embodiment . according to the second embodiment , the gaps 8 e located at the outer peripheral side of the end plate 8 b serve as drain holes . consequently , water remaining between the recess 8 c and the rectifying cover 22 can reliably be discharged . fig7 to 9 illustrate a third embodiment of the invention . in the third embodiment , similar or identical parts are labeled by the same reference symbols as those in the first embodiment . referring to fig8 , the drum support 23 has an inner surface facing the bottom of the recess 8 c . the inner surface of the drum support 23 is formed with reinforcing ribs ( a reinforcing corrugated portion ). the drum support 23 further has an outer surface which is a side opposite the side thereof facing the bottom of the recess 8 c . the outer surface of the drum support is substantially planar . the drum support 23 has a flange 23 b ( see fig8 ) formed on the outer periphery thereof so as to close the opening of the recess 8 c . the protrusions 23 b of the drum support 23 have respective distal ends ( or portions located at the outer peripheral side of the drum 8 ) formed with holes 23 c . in the above - described construction , the drum support 23 is mounted on the drum 8 so that the ribs 23 a face the end plate 8 b side ( the bottom of the recess 8 c ) as shown in fig9 . as a result , the opening of the recess 8 c is closed by the drum support 23 and the flange 23 b of the drum support 23 . the other construction of the washer - drier of the second embodiment is substantially the same as in the first embodiment . in the third embodiment , the drum support 23 is disposed in the recess 8 c of the drum 8 so that the reinforcing ribs 23 a of the drum support are face the end plate 8 b side and so that the end plate 8 b and the drum support 23 are substantially co - planar . accordingly , rotational resistance can be reduced when the drum 8 is rotated at high speeds in the dehydration step , whereupon noise can be reduced . since the rectifying cover 21 employed in the first embodiment is eliminated particularly in the third embodiment , the number of components can be reduced and accordingly , a cost reduction can be achieved . furthermore , further noise reduction and further power consumption can be achieved since the flange 23 b is provided on the drum support 23 so as to close the opening of the recess 8 c . the flange 23 b may or may not be provided although the drum support 23 is provided with the flange 23 b in the third embodiment . the invention should not be limited to the embodiments described above with reference to the accompanying drawings . the embodiments may be modified or expanded as follows . in the first embodiment , the recess 8 c is formed in the end plate 8 b of the drum 8 . the drum support 11 is accommodated in the recess 8 c . the drum support 11 is then mounted on the drum 8 . however , the drum support 11 may be mounted on the drum 8 without provision of the recess 8 c in the end plate 8 b . in this case , a rectifying cover may be mounted on the drum 8 and preferably has such a circular plate shape as to cover the entire end plate 8 b or has substantially the same size as the end plate 8 b . furthermore , as shown in fig1 and 11 , the recess 8 c of the drum 8 has an opening edge formed with a stepped portion 8 d which has substantially the same thickness as the rectifying cover 21 . the rectifying cover 21 may be fitted with the stepped portion 8 d . in this case , the rectifying cover 21 is preferably recessed slightly relative to the face of the end plate 8 b . as the result of the aforesaid construction , the difference corresponding to the thickness of the rectifying cover 21 is resolved and the rectifying cover 21 is slightly recessed . consequently , since resistance of wind against the end face of the rectifying cover 21 can further be reduced during high speed rotation of the drum 8 , noise can further be reduced and power consumption can further be reduced . additionally , a packing may be provided on the end face on which the stepped portion 8 d is in contact with the rectifying cover 21 . furthermore , the gaps 8 e are defined between the outer periphery of the recess 8 c and the rectifying cover 22 . however , as shown in fig1 , drain holes 21 b may be formed in distal ends of the protrusions 21 b ( near the outer periphery of the drum 8 ). each drain hole 21 b may take any shape even if water is allowed to pass therethrough . for example , each drain hole 21 b may be a notch . the invention is applied to the drum washer - dryer of the front loading type in each of the foregoing embodiments . however , the invention may be applied to a drum washer - drier of the top loading type . the foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense . various changes and modifications will become apparent to those of ordinary skill in the art . all such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims .