PURPOSE: To protect load from abnormality in the condition insulated from an AC power source without providing an insulating circuit, a creeping distance for insulation, or a space distance.

CONSTITUTION: This circuit is provided with a switch element 15 for cutting off power supply, which is inserted in a primary AC line 14, a current detecting circuit 16, which detects the current of the primary AC line 14, a voltage detecting circuit 18, which detects the voltage of the AC power source, a CPU 19, which monitors the detection results of both detection circuits 16 and 18 and detects the occurrence of load abnormality or power abnormality, and a memory 20, which retains the detected information of the CPU 19 until it is reset. Moreover this is equipped with a CPU 19 which judges the condition in which neither abnormality is detected at power ON of the AC power source based on the detected information and the retained information of the memory 20 and turns on the switching element 15, and turns off the switch element 15 on occurrence of either of both abnormalities during supply of AC power and writes the detected information into the memory 20, and a power circuit 17 exclusively used for a protective circuit, which gives a drive power to the CPU 19, etc.