To enable simplification of a braking mechanism.

In attracted condition attracting a brake plate 13 of a manual revolving shaft being accompanied by the action of a magnet 15, the attraction force of the magnet 15 overcomes the pressure force of a compression coil spring 24 working on the brake plate 13, and the brake plate 13 is separated from a brake plate 14 of the revolving shaft 6 at motor side and become separated state. In the separated state, a braking mechanism 16 reaches a first brake plate P braking the brake plate 13. When the attraction for the brake plate 13 of the manual revolving shaft is released being accompanied by the action of the magnet 15, and becomes the attraction releasing state, the pressure force of the compressed coil spring 24 works on the braking plate 13, the brake plate 13 is connected to the brake plate 14 of the revolving shaft at motor side, and becomes the connected state. In the connected state, the braking mechanism 16 reaches a second braking state Q in which a brake plate 20 brakes the brake plate 14 via the brake plate 13.