PURPOSE: To provide the filter processing circuit used by a data system of a bit stream form in which a sampling rate of input data is used and desired filter processing is attained with a small circuit scale.

CONSTITUTION: The filter processing circuit is used for a data signal system of 1-bit stream form, a digital filter 21 to apply desired filter processing to input data is a digital version of an analog filter configuring a switched capacitor circuit operated by a sampling rate of the input data in which an equation of charge mobile for each sampling period representing the input output characteristic is calculated digitally by the sampling rate. Multi-bit output data obtained by the digital filter 21 are converted again into 1-bit stream data by a ΣΔ modulator 22.