To obtain a ground-leakage breaker, whereby a main circuit can be broken surely, independently of the generation timing of ground leakage and the reverse connection of the main circuit is made possible, without having to increase the size of the trip coil of the circuit breaker.

In the ground-leakage breaker 1, an H-level signal is outputted from a square-wave circuit 8 during the power-supply waveshape of a half-wave rectifying circuit 7 which is 0 V; while an H-level signal is outputted from an output terminal 21 of a ground-leakage detecting circuit 4, when the detected current of a zero-phase current transformer 3 exceeds a predetermined value. When both the outputs of the square-wave circuit 8 and the ground-leakage detecting circuit 4 are H-level signals, a thyristor 10 is turned on by an AND circuit 9 outputting the H-level signal to the gate of the thyristor 10, so as to make an opening/closing contact 5 of a main circuit 2, turned off by applying a current to a trip coil 6.