PURPOSE: To reduce the size and power consumption of the filter by feeding the output signal of a primary low-pass filter to the inverted input terminal of an operational amplifier which forms the primary low-pass filter through a noninversion type integrator and a resistance.

CONSTITUTION: The output signal of the primary low-pass filter 2 is fed back to the inverted input terminal of the operational amplifier 4 through the noninversion type integrator 3 and resistance 21. Namely, the output signal is fed back to the inverted input terminal of the amplifier 4 without being shifted in phase. Thus, the biquad type secondary band-pass active filter is formed and then the noninversion integrator 3 functions as a conventional amplifier and an inversion type integrator, so the same functions that a conventional filter has are obtained. Further, operational amplifiers are reduced in number to two, so the size and power consumption of the filter are reduced.