To eliminate voltage fluctuation at a power receiving end which is to be caused by voltage drop when load changes, stabilize running performance, and enable not dynamic braking but regenerative braking, in a battery floating charge system using a step-up chopper.

By making it possible to supply power to a running motor circuit 1 from an aerial line power source and a battery BAT, voltage fluctuation at a power receiving end is prevented, and running performance is stabilized. By a step-up type battery floating charge device 2, it is made possible to step up a voltage of the aerial line power source and charge the battery. Power regeneration from the running motor circuit 1 to the battery is enabled. In the case of service interruption, self power running is enabled by the battery.