A motor has a board-retaining part that is attached in an opening portion of a gear housing with a circuit board received in the board-installing portion of the gear housing and that restricts the circuit board to move to a counter-insertion side thereof in an insertion direction of the circuit board. The board-retaining part can be attached to any position not to bring that in contact with the cover member in the direction of the center axis. Thus, in a case of installing the circuit board through the opening portion of the gear housing and blocking the opening with the cover member, it is possible to secure a seal quality of the cover member and to prevent the circuit board from rattling even when a dimensional error is introduced both in approximating and detaching directions of the circuit board and the cover member.