A leakage detector is provided with the addition of an output control circuit that monitors a circuit wire-to-ground voltage, which is at the root of a suffered operation and produced between a transformer B-class grounding phase of a monitored circuit and a D or C-class grounding electrode or a ground structure etc. of an electrical equipment connected to the grounding electrode, execute a phase judgment of a leakage current detected by a zero-phase current transformer on the basis of the monitored voltage, and stop an output operation of the leakage detector when the leakage current is a suffered current flowing from a load side L of the detecting zero-phase current transformer toward the power side K, i.e. the transformer and when the circuit wire-to-ground voltage exceeds an appropriately-established dynamic sensitivity voltage value.