A first drive cam groove extends from a drive cam specific position to one side in a circumferential direction. A second drive cam groove extends from the drive cam specific position to the other side in the circumferential direction, and an inclination angle of a groove bottom with respect to one end surface of the drive cam main body is larger than that of the first drive cam groove. A first driven cam groove extends from a driven cam specific position to one side in a circumferential direction. A second driven cam groove extends from the driven cam specific position to the other side in the circumferential direction, and an inclination angle of a groove bottom with respect to one end surface of the driven cam main body is larger than that of the first driven cam groove.