rotational speeds of the engine 12 and the electric motor 13 in step s 3 referred to as the rotation synchronization is started when the rotational speed of the engine 12 is changed from the rotational speed during idling to almost the same speed as the rotational speed of the electric motor 13 the clutch 12 is engaged step s 5 and then the mode is switched to the assistance driving mode or the engine driving mode step s 7 as a result of that the necessary power is transmitted to a tire 12 according to the hybrid vehicle 1 when it is estimated that the driver 39 s request torque exceeds the maximum torque of the electric motor 13 the driving mode is switched to the assistance driving mode or the engine driving mode even if the electric motor driving mode is performed thus the torque corresponding to the request torque can be outputted in other words when the request torque exceeds the maximum torque of the electric motor 13 the torque can be complemented by the power of the engine 12 thus the electric motor 13 and a peripheral device such as the inverter 14 do not need a capability to generate.