PURPOSE: To reduce a circuit scale by selecting a capacitor in a switched capacitor filter(SCF) with a switch at a micro computer and selecting a clock frequency for driving an SCF.

CONSTITUTION: A signal including all mode frequencies is inputted to an SCF 1. A micro computer 2 sends a control signal to select a necessary mode frequency to the SCF 1 and a clock frequency generator 3 for driving the SCF. The generator 3 generates a clock frequency corresponding to a control signal, sends it to SCF 1, further, selects a switched capacitor array(SCA) of the SCF 1 by the control signal. The necessary mode frequency is outputted from the SCF 1. Thus, the capacitor in the SCA is selected with a switch by the micro computer 2, the clock frequency for driving the SCF of the generator 3 is also selected and thus, the circuit scale is reduced.