A first buttery supplies power to an electrical load of a vehicle when an engine is in a normal operation. A second buttery supplies power to the electrical load of the vehicle when the engine is in an economical operation. A voltage regulator regulates voltages of the first buttery and the second buttery. A current limiter limits a current value flowing from the voltage regulator to the second battery to a limiting value. An engine stopping unit stops the engine when a first predetermined condition is established. An activator starts the engine when a second predetermined condition is established. A current detecting unit detects the current value when a second battery is charged. A changing unit changes a limiting value between a first limiting value and a second limiting value which is higher than the first limiting value according to the detected current value in a case where the voltage of the second battery is no more than a second predetermined value and the voltage of the first battery is no less than a first predetermined value.