PURPOSE: To reduce hunting in output of a phase compensating circuit with a short limiting time, and keep a restrictive effect on a power fluctuation in a reactive power compensator, by determining reactive power for compensation through a lead phase signal when the power in a power system changes step by step.

CONSTITUTION: A reactive power compensator is used for compensating reactive power to restrict a fluctuation in feed-line power. The reactive power compensator includes a phase lead compensating circuit 31 made up of a reset filter, a phase compensator and a limiter, and a phase lag compensating circuit 32 made up of a sign change unit, a reset filter, a phase compensator and a limiter, a disconnection detector 33 for generating a switching signal when a breaking signal for a generator is transmitted, a timer 34 for holding an output from the disconnection detector 33 for a given time, and a switch 35 for switching an output of a power fluctuation restrictive circuit from a phase lag signal (B) to a lead phase signal (A) according to the output of the timer 34. Then, a fluctuation in power in the feed line can be restricted.