To stop the operation when detecting the abnormal state of a coil.

This rat-preventing apparatus generating intermittent pulsed electromagnetic field through one or more coils CL1 leads the pulsed electromagnetic field to a power line in a building through each magnetic core coupled with the coil. A microprocessor IC1 is connected to the coil(s) to automatically detect the cycle rate of line voltage and to precisely control a coil-switching circuit. The microprocessor IC1 can detect the abnormality of the coil(s) such as short-circuit or open-circuit by being provided with coil supervisory signals. When the above abnormality was detected, the microprocessor IC1 disconnects control signals to the coil CL1 and an indicator LED1 until a normal state of the coil(s) is detected.