The objective of the present invention is to provide an earth leakage circuit breaker which is capable of reliably detecting a leakage current of an alternating current component in a circuit as well as a leakage current of a pulsating direct current component and capable of blocking the circuit in response to the leakage current. The earth leakage circuit breaker according to the present invention comprises: a leakage current detection unit for outputting a leakage current detection signal according to the leakage current from a circuit; a conversion unit for outputting the leakage current magnitude of a fundamental wave component, a ratio of a third harmonic component, and a ratio of a positive pole peak current value to a negative pole peak current value, on the basis of the leakage current detection signal outputted from the current detection unit; and a control unit for comparing the leakage current magnitude of a fundamental wave component, the ratio of a third harmonic component, and the ratio of a positive pole peak current value to a negative pole peak current value, outputted by the conversion unit, with predetermined reference values to determine whether or not a leakage current of the alternating current component is generated or a leakage current of the direct current component is generated and to thereby output a trip control signal when it is determined that the leakage current of the direct current or alternating current component is generated.