PURPOSE: To form an inexpensive anti-aliasing filter with small size tacking to a sampling frequency by using a switched capacitor filter and a programmable analog filter.

CONSTITUTION: A low pass filter section 10 consists of a low pass filter LPF1 (11) of an anti-aliasing filter of the sampling system of a switched capacitor filter itself, a 2nd low pass filter LPF 2(12) comprising the switched capacitor filter being a core of the low pass filter section and a 3rd low pass filter LPF 3(13) being a low pass filter for smoothing. A control section 20 gives a control signal and a control data required for each filter or the low pass filter section 10. Thus, the anti-aliasing filter for a switched capacitor filter and the smoothing filter whose impedance is varied with a sampling frequency FS, are obtained.