To achieve cost reduction and also to further improve operational stability, by using an element of low withstand voltage as a power semiconductor device for an inverter.

Power storage devices 21-24 are connected respectively to a DC link of the inverters 11-14, while motors 31-34 are connected to an AC link. The inverters and the power storage devices are connected in series and a main circuit is made to be a multiple series circuit. Six contactors and one filter capacitor are connected to each inverter. The power storage devices are composed of storage elements 9 and DC/DC converters 10 respectively. The withstand voltage value of the power semiconductor device used for the inverter is determined on the basis of an output voltage of the DC/DC converter 10 of the power storage device. Since four storage devices 21-24 are provided, the output voltage of the DC/DC converter 10 can be so regulated as to be equivalent to 1/4 of the voltage of an overhead line 1.