A joint includes a rotation transmitting portion and a stopper portion. The rotation transmitting portion abuts on a relative rotating portion in a circumferential direction. The stopper portion is capable of abutting on the relative rotating portion to restrict an axial position of the relative rotating portion. The stopper portion of the joint which rotates at the same speed as the relative rotating portion restricts an axial position of the relative rotating portion, whereby a sliding movement does not occur between the relative rotating portion and the stopper portion. It can be restricted that a power transmission efficiency is decreased and an abrasive wear is generated.