To prevent invalidated regeneration of an electric vehicle and to protect an electric double layer capacitor against overvoltage without requiring a load resistor facility and without increasing the capacity of a capacitor in a power storage unit where electric power supply to a powering electric vehicle and absorption of regenerated power are performed by charging/discharging an electric double layer capacitor using a step up/down chopper. The electric vehicle (2) has a function for reducing a regeneration current from 100% to 0% at the pantograph point voltage of a specified level or above according to that voltage. The control section (4C) of a step up/down chopper (4B) performs invalidated regeneration prevention control for increasing the feeder voltage up to such a level as to actuate regeneration current reducing control function of the electric vehicle (2) when an electric double layer capacitor (4A) is charged up to an arbitrary voltage.