In a state where a second power transmission path of transmitting power from the second planetary gear to the cam driving gear through the intermediate gear is selected, when the intermediate gear is opposed to the non-tooth portion for the release position of the cam driving gear, the rotation direction of the driving motor is changed to select a first power transmission path of directly transmitting power from the first planetary gear to the cam driving gear, the non-tooth portion for the release position deviates from the opposed position of the intermediate gear, and the rotation direction of the driving motor is changed again to select the second power transmission path.