PURPOSE: To protect the track circuit in a DC section and to reduce harmonics of input current in an AC section independently by providing means for setting the inductance of a filter reactor independently for DC and AC sections.

CONSTITUTION: In an AC section, an AC/DC changeover switch 2 functions to feed an AC voltage, being applied between a pantograph 1 and a wheel 3, to a transformer 4 where the voltage is stepped down. It is then rectified through a converter 5 comprising thyristors 51, 52, 53, 54 and a DC voltage 15 fed through a powering/regeneration changeover switch 6 to a filter circuit 7 comprising a filter reactor 71 and a filter capacitor 72. In a DC section, a DC voltage being applied between the pantograph 1 and the wheel 3 is fed to the filter circuit 7 through an auxiliary reactor 11. Since the inductance of the filter reactor can be set independently for the AC and DC sections, harmonics of input current can be reduced in the AC section while simultaneously the track circuit signal can be protected against interference in the DC section.