To provide an active filter for improving a harmonic current generated from a capacitor-input type rectifier as a load on a power line.

The active filter is provided with a pump-up charge circuit, an energy recovery circuit, and an abnormal voltage suppression circuit, which are added between terminals 3 and 4 of a bridge formed of switch elements 12, 13 and diodes 14, 15. The pump-up charging circuit consists of a switch element 16 and a reactor 5 for charging. The energy recovery circuit consists of a pulse-width modulated switch 17, a discharging reactor 8, and a compensation capacitor 6. The abnormal voltage suppression circuit consists of a capacitor 19, a resistor 18 and a diode 20.