PURPOSE: To suppress the outflow of harmonic current component which is not completely absorbed by a passive type filter, to a power system, by setting an active type filter consisting of a harmonic detecting circuit and a compensating harmonic impregnating circuit.

CONSTITUTION: Specific harmonic current component included in load current IL flowing to a harmonic generating load 2 is absorbed by a passive type filter 3. Besides, harmonic current component in system current IS flowing to a power systam 1 is detected by a harmonic detecting circuit 4. So far as the detection is concerned, the system current 15 is detected by a rectifier 6 and is Fourier- decomposed, or fundamental current component only is avoided. By this method, with compensating harmonic voltage VC in proportion to the amplitude of the harmonic current component detected by the harmonic circuit and with phase opposite to that of the harmonic current component, the power system 1 is impregnated by a compensating harmonic impregnating circuit 5, and the outflow of the whole harmonic component to the power system 1 is suppressed further.