PURPOSE: To contrive to make the performance of a DC-AC converter higher by using a GTO thyristor as the switching element of a nonmultiple AC-DC converter and a transistor as the switching element of the DC-AC converter and by increasing the breakdown strength of the GTO thyristor 1.3 times or more than that of the transistor.

CONSTITUTION: In a nonmultiple PWM control-type AC-DC converter 4, a high- frequency GTO thyristor is adopted as a switching element so that a ripple generated in a supply current is small. Also, an inverter using a transistor as a switching element is adopted in a DC-AC converter 6 so that a PWM control signal can be made into a high frequency. Further, even if a surge voltage such as direct lightning is generated in an electric overhead line 1, the surge voltage does not bring about the destruction of the switching elements because the breakdown strength of the GTO thyristor is increased 1.3 times or more than that of the transistor. Thus, it is possible to make the performance of a DC-AC converter 6 higher.