A first internal gear of a speed reducer includes an internally-toothed portion and a bearing portion and is formed as a one-piece member that is formed separately from a first housing. The internally-toothed portion forms internal teeth, which are meshed with external teeth of a first planetary gear. The bearing portion includes an eleventh cylindrical surface, which supports a motor shaft. The internal teeth of the first internal gear are arranged coaxial with the eleventh cylindrical surface. The internal teeth of the first internal gear and the bearing portion are formed as portions of the one-piece member.