PURPOSE: To facilitate the alteration of setting of a circuit breaker tripping current as the load capacity of facilities increases and to facilitate the maintenance of the circuit breaker in receiving and transforming facilities.

CONSTITUTION: A first and second indicator lamp are provided, and a first and second pilot current value and a tripping current value, all of which can be freely set and varied, are set in a control circuit 14. A detected current value is compared with each set current value in the control circuit 14. When the circuit current is in excess of either of the pilot current values, the corresponding indicator lamp 6 or 7 is turned on, whereas when the detected current value is equal to or greater than the tripping current value, the current is tripped to a circuit breaker via an operating circuit 16.