A phase-control switchgear includes a circuit breaker, a phase difference detection unit, a storage unit, and a circuit breaker control unit. The phase difference detection unit detects a phase difference between voltages of a specific phase (U-phase) of buses to which three-phase generators are respectively connected, at a plurality of time points. The storage unit stores the detected phase differences. When the three-phase generators are out of synchronization, the circuit breaker control unit estimates a breaking time point at which the phase difference between the voltages of the U-phase of the buses will be in the range of not less than −80° and not more than 80°, based on the phase differences at the plurality of time points stored in the storage unit. The circuit breaker control unit opens the circuit breaker to break a current at the estimated breaking time point. This makes it possible to suppress a transient voltage generated between electrodes of the circuit breaker after the current is broken.