A socket receives charging voltage and auxiliary voltage of the main battery from an external power supply. A charging line Lch connects the charging voltage to the main battery. Auxiliary power supply lines connect the auxiliary voltage to a vehicle drive control unit. A main switch is provided on a constant line for inputting the output of an electric power converting unit to the vehicle drive control unit. The vehicle drive control unit includes an electric power converting unit starting unit started when the auxiliary voltage is applied to output a starting signal of the electric power converting unit, and means for maintaining the starting signal to charge the sub-battery with the electric power from the electric power converting unit when the voltage applied from the electric power converting unit through the main switch to the vehicle drive control unit is a predetermined value.