A device configured to actuate a driven member by driving a driving motor (11) includes a brake which does not consume electric power and which can be easily mounted in the device. A speed reducer is mounted in the device, and includes a reduction mechanism (2) for transmitting the rotation of the driving motor (11) toward the driven member after reducing its speed, and a locking type reverse input shutoff mechanism (3), as the brake, which is configured to mechanically lock up when reverse input torque is applied from the driven member while the driving motor (11) is not being driven, thereby retaining the position of the driven member. The reduction mechanism (2) and the reverse input shutoff mechanism (3) are combined to constitute a single unit.