surface of the rear wall 110 of the tub 102 has a plan or slope having no convex or concave portions in the rotating direction a of the drum 103 this is because the reinforcing portions 130 are formed in the circumferential direction of the tub 102 corresponding to the rotating direction a of the drum 103 now how the entire inner surface of the rear wall 110 of the tub 102 may be planar without any convex or concave portions in the rotating direction a of the drum 103 will be described with reference to fig8 the reinforcing portions 130 naturally provide the outer rim region 113 of the tub 102 with a convex and concave portion with respect to a radial direction b of the tub 102 however the reinforcing portions 130 protrude in the rotating direction a of the drum 103 from the outer rim region 113 of the tub 102 to have a predetermined semi circular shape and therefore define no convex or concave portions with respect to the rotating direction a of the drum 103 accordingly the reinforcing portions 130 exert no resistance on the flow of air caused between a rear wall 103 a of the drum 103 and the rear wall 110 of the tub 102 during rotation of the drum 103 consequently the reinforcing portions 130 further reinforce the tub 102 and also.