A clutch is provided with a drive-side rotational body and a driven-side rotational body, which can move in the axial direction between a coupled position and a decoupled position. The driven-side rotational body has a groove having a helical portion and an annular portion that is deeper than the helical portion. The driven-side rotational body is urged toward the coupled position by an urging member. The driven-side rotational body is moved to the decoupled position against the urging force of the urging member by insertion of a pin into the helical portion. A projection is provided on the tip of the pin, and a recessed groove for accommodating the projection when the pin is inserted into the helical portion is provided in the bottom surface of the helical portion.