An output shaft is configured by connecting a first shaft and a second shaft, coaxially arranged with each other, by a reverse input cutoff clutch 20; an end portion on one side in an axial direction of the second shaft located on an opposite side from the first shaft with a gear portion sandwiched in between in the axial direction being rotatably supported with respect to a fixed portion by a bearing device; the reverse input cutoff clutch having a function that, when rotational torque is input to the first shaft, transmits the rotational torque input to the first shaft to the second shaft, and when rotational torque is reversely input to the second shaft, completely cuts off the rotational torque reversely input to the second shaft and does not transmit the rotational torque to the first shaft, or transmits part of the rotational torque to the first shaft and cuts off the remaining portion.