To protect the inverters and motor generators from damage caused by abnormal currents resulting from the sudden changes in voltage that occur when changing the battery voltage. A vehicle equipped with an engine 10* and first and second motor-generators 11 and 12 that can generate electricity by being driven by engine 10* or from regeneration of kinetic energy of the vehicle, power supply line 25 that connects first motor-generator 11 with second motor-generator 12, and battery 23 connected via switch 24 in the middle of electric power supply line 25. When changing the voltage of battery 23, switch 24 is opened before the voltage of battery 23 is changed, and switch 24 is closed only after one of the motor generators 11 and 12 is caused to generate electric power or propel the vehicle in order to reduce the difference in voltage between power supply line 25 and battery 23.