A first engine ENG1, transmission TM1, one-way clutch OWC1, driving target member 11 connected to an output member 121 of the one-way clutch, main motor/generator MG1 connected to the member 11, sub motor/generator MG2 connected to an output shaft S1 of the engine ENG1, battery 8, and controller 5. The controller 5 performs EV running, engine running, and series running where power generated by a sub motor/generator MG2 using the power of the first engine ENG1 is supplied to the main motor/generator MG1. Series running is carried out between EV running and the engine running when switching from EV running to engine running is carried out. A rotational speed of the engine and/or a transmission ratio of the transmission are/is controlled so that the rotational speed input to the input member is less than the rotational speed of the output member 121 during the series running control.