A rotating device 1 according to the present application includes a motor 3, a gear 5 that transmits rotation of the motor 3 to an external device, and a sensor 7. The sensor 7 includes a sensor part 70 and a housing 72 that accommodates the sensor part 70. The sensor part 70 is capable of detecting a rotational speed or a rotational angle of the gear 5. The gear 5 includes a recess 50 in a rotational axis direction of the gear 5. The recess 50 accommodates a part of the housing 72.