A switching controlgear of circuit breaker 100 outputs an opening command signal or closing command signal to the circuit breaker with the maximum being 1 cycle or less of wait time when the opening command signal or closing command signal is detected, and can cause the circuit breaker to open or to close at a desired phase of the main circuit current or power system voltage. The switching controlgear of circuit breaker 100 has switching control signal output time calculation means 10 and switching command signal output delay means 20. The switching control signal output time calculation means 10 calculates the switching control signal output time using the detection timing of the opening command signal or closing command signal as a reference so that the circuit breaker opens or closes at the desired phase after the total time of the switching control signal output time and the estimated opening operation time or estimated closing operation time of the circuit breaker 620 is elapsed. The switching command signal output delay means 20 outputs a delay-controlled opening command signal or a delay-controlled closing command signal to the circuit breaker after the switching control signal output time, which is the latest, is elapsed when an opening command signal or closing command signal is actually detected.