PURPOSE: To prevent any noise from being generated in an output when the titled circuit enters the selecting state by fixing a level of a terminal of a circuit characteristic variable capacitor not selected to a specific voltage level so as to prevent the electric charge from being stored to the terminal during the non-selection period.

CONSTITUTION: Switches S5, S6 are used to changeover the selection/nonselection of an input capacitor C1, the capacitor C1 is connected to an inverting input of an operational amplifier 1 by the contact of the S5 at the selection state and the terminal of the capacitor C1 is grounded via the switch S6 to prevent the open state at the non-selection state. The changeover switches S7, S8 are used for the input capacitor C2 for the similar purpose and changeover switches S9(S11) and S10(S12) are used for DC feedback capacitors C3(C4). Thus, the voltage at the terminal of the capacitor not selected is fixed and an electric charge is stored to the capacitor.