ELECTRIC CIRCUIT DIAGNOSING APPARATUS

PROBLEM TO BE SOLVED: To provide an electric circuit diagnosing apparatus which does not fail in the deterioration diagnosis due to deterioration of the capacitance reduction but diagnoses the deterioration of an apparatus under test, without direct measurements. SOLUTION: An apparatus 4 under test, a normal apparatus 3 and two resistance elements 11, 12 of the same resistance value are assembled in a bridge circuit 2, a switch 1 is set on to apply a voltage to the bridge circuit 2, while a balance detector circuit 17 detects the characteristic change in the transition of the voltage application, thus directly comparing the apparatus 4 under test with the normal apparatus 3 to determine the deterioration of the apparatus 4 under test. This has no need of providing any separate test terminal but only needs to connect an input/output contact 13a of the apparatus 4 under test to connection terminals 13 of the bridge circuit 2.