To provide a structure for making drum cylindrical diameter more efficient to the maximum by properly setting a position of a drum driving device for an effective use of the installation space in a basement.

A large sprocket 7 is provided between a central cylinder 3 with the largest diameter and right and left rear roller bearings 6 of a rear cylinder 4, and the large sprocket 7, a chain 8, a small sprocket 9 and a motor 10 are installed within the total width of the central cylinder 3.