PURPOSE: To process a signal having various signal speeds at a low output noise by connecting a circuit having a switch and a capacitor operated at a frequency MfS (1<M) to an input terminal or an output terminal of an operational amplifier.

CONSTITUTION: The circuit having the switches 101, 102 and the capacitors 103, 104 operated at a frequency MfS (1<M) is connected to an input terminal or an output terminal of the operational amplifier 3. The switches 101, 102 are driven by clocks 10 and 20. M-set of sample values are added to the capacitor 103 at one period of the clocks 1, 2 with respect to noise component. M-set of noise samples are added also to the capacitor 104 and averaged. Thus, the signal having various signal speeds is processed with low output noise.