A target driving power is calculated in accordance with the operating condition, a fuel consumption rate per power unit is calculated at all the possible operating points of an engine (1) and a drive motor (5) to realize the target driving power, a target fuel consumption rate is set on the basis of the operating condition, and an operating point of the engine (1) and drive motor (5) at which a fuel consumption rate that is equal to the target fuel consumption rate can be realized is searched. When an operating point at which a fuel consumption rate that is equal to the target fuel consumption rate can be realized is not found, the fuel consumption rate relating to driving power is corrected with only the fuel consumption rate relating to electric power for charging a battery device set at a predetermined value which is smaller than the actual fuel consumption rate, an operating point at which the fuel consumption rate relating to driving power reaches a minimum is selected, and the engine (1) and drive motor (5) are controlled to achieve the selected operating point.