PURPOSE: To reduce loss of a gate power source for a self-arc extinguishing element by reusing a voltage of a snubber capacitor charged by dividing a voltage between an anode and a cathode of a gate turn-off thyristor (GTO) for a gate power source of the GTO.

CONSTITUTION: A voltage between an anode and a cathode of a GTO 31 is divided by resistors 58, 59 to initially charge a capacitor 60 for a power source. Then, an output voltage of the GTO 31 is divided to charge first, second snubber capacitors 31C, 52 to constitute a snubber circuit. A discharging current of the capacitor 52 is supplied to a primary side 53A of a transistor 53 through a switching element 54 to be closed in synchronization with turn-on of the GTO 31. An output of a secondary side 53B is rectified by diodes 55, 57 to charge a capacitor 60 for a power source. The GTO 31 is turned ON or OFF by a signal from an output terminal G of a DC/DC converter 61. Thus, charge of a snubber capacitor is used to reduce loss of an apparatus.