PURPOSE: To obtain an inverter unit in which energy stored in the energy storing elements in a snubber circuit or a voltage clamp circuit can be regenerated efficiently to power supply through ON/OFF operation of a self-extinguishing semiconductor element.

CONSTITUTION: Half bridge in an inverter unit comprising GTOs 1a, 1b is connected with a clamp snubber circuit integrating a snubber circuit and a clamp circuit and having no resistance(anode reactors 3a, 3b, a snubber capacitor 6, diodes 7a, 7b, recovery capacitors 11a, 11b, diodes 14a, 14b, recovery capacitors 15a, 15b, reactors 21a, 21b). Furthermore, power regenerating units 16a, 16b for regenerating excessive energy from the half bridge to DC power supplies 12a, l2b are also provided.