To provide sufficient regenerative braking force, even if exhaust gas amount is small, in a series hybrid vehicle.

An exhaust valve 20 is provided in an exhaust pipe 9 of an engine, and an exhaust valve control unit 21 for controlling the opening is provided. In a case where regenerative electric power is consumed by motor- operating a generator, if the engine speed exceeds a first prescribed engine speed, the opening of the exhaust valve is gradually decreased, while if the engine speed exceeds the second specified engine speed, the exhaust valve is closed. Since the motor-driven generator consumes more regenerative electric power, braking force larger than conventional braking force can be obtained. Since the opening is gradually changed, the change of load torque of the engine is smoothed, and a sense of incongruity is not generated on operating feeling.