A brake-side clutch part includes an outer ring whose rotation is restricted and an output shaft from which rotation is output. The outer ring is provided with a slide gear that meshes with the output shaft when rotational torque is cut off and releases a meshing state with the output shaft when rotational torque is transmitted. The output shaft is provided with an inner gear that meshes with the slide gear so as to be slightly rotatable. An alignment part that aligns a phase of the inner gear with that of the slide gear when rotational torque is cut off, and a centering part that returns the inner gear to a neutral position with respect to the output shaft when rotational torque is transmitted are provided between the inner gear and the output shaft.