A gear with an annular member disposed alongside a side wall of an inward protrusion in a manner turnable relative to the side wall. The annular member is formed with abutment projections with inclined surfaces extending in circumferential directions and engaged by engaging pawls. The annular member is urged by return springs in such a manner that the portion of each abutment projection, at least other than the inclined surfaces, overlaps each engaging projection as viewed in axial direction. Each inclined surface of the abutment projection is made up of a bottom-side inclined surface having an inclination angle allowing abutment by the engaging pawls, and a top-side inclined surface having an inclination angle not allowing abutment by the engaging pawls but causing sliding movement of the engaging pawls. The engaging pawls are prevented be imposed with excessive local load when the engaging pawls engage the engaging projections of the gear.