PURPOSE: To extract an abnormal circuit easily by a system wherein a detection signal is subjected to time supervision, and when a change in time of its on/off operation exceeds a given range, the circuit is determined as abnormal.

CONSTITUTION: Electromagnetic relays 10, 20 30 and relay contacts 11, 21, 31 are provided for circuits 12, 22, 32 to test, and a current is carried to each circuit by turning the electromagnetic relays on according to signals a1, a2, a3. Then, motors 13, 23, 33 are provided as output loads for each circuit; when an output of each circuit is turned on, relay contacts 15, 25, 35 are also turned on, thus obtaining output signals b1, b2, b3.