To provide an electronic tripping circuit and a regulator for circuit breaker, which can facilitate regulating work and has diagnostic functions as well.

This electronic circuit breaker 20 is provided with a memory section 29, which permits overcurrent tripping characteristic data to be written, and a regulating terminal section 31 for writing the data of the memory section 29 from the outside. The regulation terminal section 31 connected to IC 4, can monitor a current value I24, into which energizing current of a cable run 21 is converted. A regulator 40 is connected to the electronic circuit breaker 20 through the regulating terminal section 31 and adds a difference ΔI between the first current value I24 with IC 24 and a second current value I41 of the cable run with a highly precise CT 50 to the current parameters of overcurrent tripping characteristic data, for correcting the overcurrent tripping characteristics data.