To save a space more by relatively shortening a part of a low-speed side shaft corresponding to a bearing and a one-way clutch.

The one-way clutch such as a roller clutch 150 is interposed between an outer diameter side of the low-speed side shaft 3 and a cylindrical part (low speed side power transmitting member) 4a of a disk-like member 4 of an outer ring 32. A single-row ball bearing 170 is interposed between the outer diameter side of the cylindrical part (low speed side power transmitting member) 4a of the outer ring 32 and a housing 1. With this structure that the roller clutch 150 and the single row ball bearing 170 are arranged to be overlapped with each other in the radial direction, a part of the low speed side shaft 3 corresponding to the single row ball bearing 170 and the one-way clutch 150 can be relatively shortened in the axial direction.