Inverter device for driving multi-phase ac motor

Although there are a technique for detecting the failure of an arm circuit of each phase and an operation technique using only a normal phase, the present invention addresses the problem of the occurrence of a brake torque caused by the closed circuit of a failed phase. An inverter device for driving a multi-phase AC motor is provided with a first power supply switching element (15) provided in the power line to an inverter circuit, a second power supply switching element (35) provided for each phase of arm circuits of the inverter circuit, and a motor relay switching element (34) provided in the output path from each phase, wherein the parasitic diodes of the first power supply switching element (15) and the second switching element (35) have different direction characteristics to prevent the formation of a closed circuit.