To prevent an overcurrent protection circuit from being operated again due to a rush current to a snubber capacitor when overcurrent protection operation is canceled, by turning on a specific switching element and forming the charging path of the snubber capacitor after the overcurrent protection circuit is operated and all high-frequency switching elements are turned off.

An overcurrent protection circuit 25 compares an input current being detected by DCCTs 26-28 with a protection level, and outputs a protection operation command 29 for turning off all high-frequency switching elements IGBT1-12 when an overcurrent is detected. On the other hand, a comparison circuit 34 compares the AC input phase voltage of each phase with 0 V and generates a section signal 30. In this case, a logic circuit 31 outputs a drive pulse 32 for turning on only the IGBT in a phase with the largest phase voltage, breaks the load current of an SMR converter, and at the same time secures a charge circuit to a specific snubber capacitor out of snubber capacitors 19-21, and prevents a rush current from occurring when a protection operation is canceled.