A cylindrical ring gear has first external teeth and a support portion in an axial direction of the cylindrical ring gear. An output shaft extends through the cylindrical ring gear and is supported to rotate concentrically with the cylindrical ring gear. A disconnect mechanism is configured to connect or disconnect an inner periphery of the cylindrical ring gear to an outer periphery of the output shaft based on a moved position of the movable engagement member. An actuator is disposed such that the first external teeth are located between the support portion and the actuator. The actuator is configured to move the movable engagement member between a connection position and a disconnection position. The cylindrical ring gear is coupled to the output shaft so as to be relatively non-rotatable in the connection position. Relative rotation between the cylindrical ring gear and the output shaft is allowed in the disconnection position.