PURPOSE: To eliminate the loss due to the switching of a converter and to improve the operation efficiency by stopping sending gate driving pulses to the converter when the device is operated with its reactive power output of nearly zero.

CONSTITUTION: A dead zone 401 for stopping (GB) the gate pulses when the reactive power output of the self-exciting reactive power compensating device (self-exciting SVC) becomes zero has a function for the GB of a self-exciting converter 3 by judging that the dead zone 401 is entered when the reactive power component of the self-exciting SVC to be outputted is almost zero and the state does not change. By entering the dead zone 401, the self-exciting converter 3 performs the GB and enters a stand-by state. Even in this case, the self-exciting SVC only stops sending the gate pulses, so the transmission of gate pulses is started immediately when out of the range of the dead zone 401 to perform system control. Even in a state where the GB is performed by entering dead zone 401, gate pulses begin to be sent out once the load of a DC capacitor is discharged and a DC voltage reference is not met.