To simply cope with fluctuation in the different width between an overhead-line voltage and an energy storage voltage by one of step-up voltage control or step-down voltage.

In a railway rolling stock, an energy storage device 4 charged according to the running by the supply of power from an overhead-line 8 is installed in an overhead-line section, the running is made by the supply of power from the energy storage device 4 in a section without the overhead-line, and charging from the overhead-line 8 to the energy storage device 4 is controlled by providing a difference -VA(-VA) between a nominal voltage VK0 of the overhead-line voltage VK and a nominal voltage VB0 of the energy storage voltage VB.