PURPOSE: To suppress higher harmonic extension owing to parallel resonance without damaging higher harmonic absorption by series resonance, by connecting a damping resistor in parallel with a resonance capacitor, and connecting a resonance reactor in series to this parallel connection circuit.

CONSTITUTION: A damping resistor 123 is provided as a parallel damping circuit in parallel with a resonance capacitor 121 for forming a series resonance circuit, or a series circuit composed of the damping resistor 123 and a resonance capacitor 121 is provided in parallel with the resonance capacitor 121, and a resonance reactor 122 is provided in series to this parallel connection circuit. Besides, a damping capacitor is connected in series to the damping resistor 123, and selection is so made that the constant of the damping capacitor may be larger than that of the resonance capacitor 121. As the result, it becomes possible to cause the whole capacitor section for forming a parallel resonance to have a damping effect. Consequently, it becomes possible to suppress higher harmonic extension owing to parallel resonance without damaging higher harmonic absorption by parallel resonance.