A three-phase inverter power supply circuit protecting apparatus includes: a power supply circuit 4 for converting an AC voltage into a DC voltage; a three-phase inverter circuit 3 for receiving the DC output as input to drive an AC motor 11; a power supply current detecting circuit 7, 13 for detecting the current of a power supply circuit 2; a circuit 10, 15 for detecting the DC input current of the inverter 3; a circuit 14 for detecting the DC input voltage of the inverter 3; an inverter input power calculating means 26 for calculating the input power of the inverter based on these DC input current and voltage; a power supply voltage anomaly detecting means 27 for performing power supply voltage anomaly judgment based on the relationship between the power supply current and the inverter input power; and a control means for halting the controls of the power supply circuit 2 and the three-phase inverter 3 in response to the anomaly judgment.