To prevent performance deterioration of the battery of a battery power source by appropriately raising the temperature of the power source by changing the depth of discharge which controls the start and stop of a power generator in accordance with the power source.

A hybrid electric vehicle is provided with a running motor 10 which becomes a driving source at the time of running the automobile, a battery power source 31, and a power generator 21 which supplies generated power to the motor 10 and power source 31. Then, the depth of discharge which controls the start and stop of the generator 21 is changed, according to the temperature of the power source 31. When, for example, the temperature of the power source 31 is lower than an appropriate value, the temperature of the power source 31 can be raised quickly to the appropriate value, so as to prevent the performance deterioration of the battery of the power source 31, by controlling the depth of discharge to make the stopping timing of the generator 21 earlier. In addition, even when the engine of the automobile is in a cold state and the heating device of the power source 31 does not function, the performance deterioration of the battery can be prevented by effectively raising the temperature of the power source 31.