A speed reducer-equipped motor includes a motor, a helical gear, an eccentric shaft, a stationary gear with a second stopper, a transmission gear, an output gear unit, and a lock gear with a first stopper. The first stopper mechanically contacts with the second stopper, thereby stopping the lock gear from revolving and rotating to stop the rotation of the output gear unit. A physical load which is generated by the contact of the first stopper with the second stopper and acts on that contact and a physical load which is generated by the contact of the first stopper and the second stopper and acts on meshed portions of teeth of the first stopper and the second stopper are oriented in opposite directions.