PURPOSE: To protect a phase-advancing capacitor by outputting an opening signal for opening a phase-advancing capacitor opening and closing means when an overload detection signal continues for previously set time.

CONSTITUTION: A current comparing means 20 compares the measurement of the current of each phase-advancing capacitor 2 with a set value in response thereto and when the measurement exceeds the set value, an overcurrent detection signal is outputted. A voltage comparing means 22 compares the voltage of an electrical power system 1 with a set value and when the measurement exceeds the set value, the overvoltage detection signal is outputted. An overload detecting means 24 detects that an overload current detection signal is outputted on condition that the overvoltage detection signal is outputted to output an overload detection signal. A timer means 30 outputs an opening signal for opening a phase-advancing capacitor opening and closing means 3 when the overload detection signal continues for preliminarily set time. Therefore, the phase- advancing capacitor 2 can be protected.