A speed reducer is configured to reduce a rotational speed of rotation generated by torque received from a drive device and output the torque of the rotation of the reduced rotational speed. A drive cam has a plurality of drive cam grooves formed at one end surface of the drive cam and is rotated by the torque outputted from the speed reducer. A driven cam has a plurality of driven cam grooves formed at one end surface of the driven cam while each of the plurality of rolling elements is clamped between a corresponding one of the plurality of drive cam grooves and a corresponding one of the plurality of driven cam grooves. At least a part of each of the plurality of drive cam grooves overlaps with the speed reducer in the axial direction.