PURPOSE: To obtain a steep filter characteristic by using a clock signal outputted from a clock circuit generating the clock signal changed in response to the change in the frequency depending on the frequency change in a filtering object signal so as to drive a switched capacitor used as a resistive element.

CONSTITUTION: The switched capacitor used as the resistive element and the clock circuit whose frequency is changed in response to the frequency change of the filtering object signal are provided to drive the switched capacitor by using a clock signal outputted from the clock circuit. For example, a clock signal Cs having a frequency equal to that of the filtering object signal is inputted to a terminal Ts, a clock signal Cm multiplying the clock signal Cs is lighted by a multiplier MP and the result is outputted to an active filter SCF using the switched capacitor as the resistive element as a drive signal. The steel filter characteristic is obtained by changing the center frequency in response to the frequency of the signal being an object to the filtering.