PURPOSE: To reduce the effect of noise due to parasitic capacitance of a switch by coupling the 2nd switch subject to switch control complementarily to the 1st switch between an equivalent resistance circuit and a ground terminal.

CONSTITUTION: The 1st equivalent resistance circuit Re1 comprising series connection of the 2 sets of the 1st switches SW 1 at both sides of the 1st leakage capacitor Cl1 and the 2nd equivalent resistance circuit Re2 comprising two sets of the 2nd switches SW2 driven in opposite phase to the 1st switches SW1 at both sides of the 2nd leakage capacitor Cl2 are coupled between the input and output terminals of an operational amplifier Amp in parallel with a storage capacitor Ca in order to saturate the stored charge in the storage capacitor Ca at a prescribed charge storage in an incomplete integration type circuit. Thus, the AC noise component injected to the 1st capacitor via the parasitic capacitance of the switch is cancelled at different polarity and the effect of noise due to the parasitic capacitance of the switches is reduced.