PURPOSE: To damp and absorb high load so as to improve durability by interposing a moving cylinder between a clutch inner and a driven shaft and engaging the inner with the moving cylinder, and the moving cylinder with the driven shaft, by means of a helical spline.

CONSTITUTION: A moving cylinder 14 is arranged inside a clutch inner 12 and an output rotary shaft 5 is inserted therein. The moving cylinder 14 and the output rotary shaft 5 are engaged each other by means of the first helical spline 14a and a tooth portion 5a. Meantime, the moving cylinder 14 and the clutch inner 12 are engaged each other by means of the secondary helical spline 14b and a tooth portion 12a. High load such as shock load applied to the output rotary shaft 5 is changed to the backward force of the moving cylinder 14, which is damped and absorbed by receiving through an elastic body 16. Thus, any damage to each component can be prevented so that durability can be improved.