The object of the invention is to travel backward by an engine alone in a state where an electric motor is disconnected. Thus, external teeth are formed on the outer periphery of a ring gear which meshes with a first sun gear via a first pinion gear and a second pinion gear and to which power input from an electric motor is transmitted; a power transmission mechanism further includes a gear meshing with the external teeth of the ring gear; and a second clutch capable of non-rotatably fixing the ring gear at the time of causing a vehicle to travel backward with power input from an engine is provided between the ring gear and a transmission case.