PURPOSE: To decrease base-line noises and base-line drifts contained in the output electric signal of an analyzing apparatus, to improve sensitivity and to obtain an analog filter device having the quick response.

CONSTITUTION: An active low-pass filter is constituted of multistage integrating circuits comprising a resistor R1 of 80-120kΩ, a resistor R2 of 40-60kΩ, capacitors C1 and C3 of 40-60μF, capacitors C2 and C4 of 400-600μF and OP amplifiers AMP1 and AMP2. An active high-pass filter is constituted of a differentiating circuit comprising a resistor R3 of 100kΩ, a resistor R4 of 200kΩ, a capacitor C5 of 400-600μF and an OP amplifier AMP 3. An analog filter device, which is constituted by connecting the active low-pass filter circuit and the active high-pass filter circuit or independently constituted of each active low-pass filter circuit and each active high-pass filter circuit, is obtained.