PURPOSE: To quicken the processing speed of the filter by supplying an input signal to an inverting input terminal of an operational amplifier via a switch switched with a 1st phase clock signal and connecting a prescribed added input capacitive element to the inverting input terminal via a switch switched with a noninverting clock signal.

CONSTITUTION: The difference from a conventional circuit resides in that capacitors CX and CY are added via a switch closed synchronously with a clock signal 1. That is, the input capacitance is C1+-C2 when the clock signal 1 is set and a clock signal 2 is reset when a 1st operational amplifier circuit Amp 1 is noticed, and the input capacitance is CX when the state of the clock signals is opposite to above. When the relation of CX=C1+C2 is set, the feedback quantity is always the same, a sufficient phase margin is obtained thereby expanding the processing enable band. When the 2nd operational amplifier circuit Amp 2 is noticed and when the clock signal 1 is set and the clock signal 2 is reset, the input capacitance is expressed as C3+C4+C"1 and when the state of the clock signals is opposite to above, the input capacitance is expressed as CY+C"1. Thus, with the selection of CY=C3+C4, the quantity of feedback is kept always constant.