A circuit and method for judging a latent short-circuit defect, also known as a short-circuit defect with time passing, in the case of a high voltage system. A detection-dedicated wiring for detecting a short-circuit defect is provided between a first high voltage system wiring and a second high voltage wiring. A power supply and an ammeter is connected in series and one end of it is connected to the high voltage system wiring and the other end of it is connected to the detection-dedicated wiring. If a current value us higher than a predetermined value when the power supply is turned on, one can judge that the circuit has a high possibility of the latent short-circuit defect.