PURPOSE: To shorten the length of a shaft to make the overall size compact by providing a second fixed member and a one way clutch arranged between a rotating member and the cylindrical part of the second fixed member.

CONSTITUTION: The inner race 218A of a second one way clutch 218 is spline- coupled with the other end of a braking shaft 212 on one end of which a sun gear 214, with a sub-input gear 202 placed between both the ends. The outer race 218B of the second one way clutch 218 is pressed and fixed into a cylindrical part 318A provided adjacent to a confining wall 318 in its axial direction as a second fixed member. The outer peripheral part of the confining wall 318 is fixed to a cover body 310 as a first fixed member confining a circular space. Further, a dish plate 220 is fixed to the end of the inner race 218A, and plural clutch plates are provided between the dish plate 220 and the cover body 310 as multi-disc frictional engaging elements.