To prevent an electric outlet from dropping into the rear side of an end plate and from being unavailable and improve assembling ability.

Each electric outlet 16 is constituted so as to be grabbed and fixed between electric outlet receiving portions 26, 27 provided at an axial end of a drum 9 and an electric outlet pressing portion 20 provided on a front end plate 10. Thus, when a power plug is inserted into or pulled out of the electric outlet 16, stress does not collect to a specific part and a screwed mounting portion does not break. The front end plate 10 is fastened to the drum 9 with a screw 31 in a state that each electric outlet 16 is placed on the electric outlet receiving portions 26, 27, and thereby the electric outlet 16 can be fixed. Therefore, assembling ability can be improved comparing with a case that the electric outlet is screwed to the front end plate.