To provide an electronic circuit breaker capable of detecting occurrence of a leakage without using a zero-phase current transformer and suppressing large-sizing of a circuit breaker case or the like.

Each of current transformers 10 is provided with a coil part 11 composed of an electric wire wound around, and an electric current flowing in the coil part 11, 11.. is measured and based on the measurement result, a predetermined vector operation is carried out to enable to detect occurrence of a leakage. As a result, the occurrence of a leakage can be detected without using a zero-phase current transformer and large-sizing of a circuit breaker case or the like can be suppressed.