PURPOSE: To provide an inexpensive power stoppage detection method, in a system which has need to detect the power stoppage of the primary side and the secondary side of, especially, an electromagnetic contactor, concerning the power stoppage detection method for an inverter system.

CONSTITUTION: This system comprises a rectifier 3, a comparator 1, and a waveform shaping circuit 12, and the power stoppage of the primary side and the secondary side of an electromagnetic contactor 10 is performed by the voltage detection of a total of three phases constituted of two phases from the primary side of an electromagnetic contactor 10 and the residual one phase from the secondary side. Hereby, the number of wirings required for power stoppage detection and the number of the parts of a power stoppage detection circuit can be reduced, so it has an effect on the cost down of the system.