To increase power factor and to provide the quality assurance of a power source through the avoidance of higher harmonics.

At the input side of a constant voltage power supply (AVR) system, a shunt reactor 15 inserted parallel in a high-pass filter circuit 11 operates in such a way as to eliminate the fundamental harmonic of a leading current. Similarly at the output side of the AVR system, a shunt reactor 6 inserted parallel in a high-pass filter circuit 8 operates in such a way, as to eliminate the fundamental harmonic of the leading current. This constitution enables inhibiting the flow of a higher harmonic current from the power supply system into the input side of the AVR system and to prevent the higher harmonic interferences generated by a load facility. Providing a simultaneous solution for the two themes of increasing power factor and protecting from the higher harmonics, this brings an energy saving effect as a whole.