Power generated by an engine is inputted to a carrier of a first planetary gear mechanism. Power generated by a motor is inputted to a sun gear of a second planetary gear mechanism. Power from a ring gear of the first planetary gear mechanism and power from a carrier of the second planetary gear mechanism are combined and transmitted to an axle of driving wheels. While power input from the engine to the carrier of the first planetary gear mechanism is maintained, rotation of a sun gear of the first planetary gear mechanism is restricted with a first clutch, a second clutch or a first brake. While power input from the motor to the sun gear of the second planetary gear mechanism is maintained, rotation of a ring gear of the second planetary gear mechanism is restricted with a second brake or a third clutch.