PURPOSE: To reduce the switching noise of a capacitor array and to enlarge the on/off ratio of a capacitance by providing a switch element controlling the continuity of an electrode and a power source and a voltage means which changes the conductive impedance of the switch means in plural steps.

CONSTITUTION: MOS Tr 161 which has the same channel length with FET switching Tr and which is the same conductive type is constant current-operated near a threshold voltage, the gate voltage is used as a potential ν0 and potential ν1 and ν2 which are slightly higher than ν0 are generated by using a diffusion resistance or passive resistors 162, 163 and an MOS resistor 164. A highest potential ν3 is set to a potential near a power source V0D. The potentials ν0-ν3 are selected by switches 171-178 and are given to a transfer gate as intermediate potentials VEE1 and VEE2. The potentials ν0-ν3 are given to the gate of the FET switch with a large time constant, and an equal capacitance is smoothly changed.