PURPOSE: To prevent gain fluctuation due to the difference in stray capacitance by grounding a connecting point between the 1st switch means and the 2nd switch means via the 5th switch means and applying switch control to the 1st∼5th switch means in a predetermined order.

CONSTITUTION: When the 2nd and 4th switches 3, 4 are turned on by the 2nd clock pulse at first from the off-state of all the 1st∼5th switches 2, 3, 6, 7 and 13, a capacitor 5 and a stray capacitor 10 are charged according to an input signal inputted from an input terminal 4. Then the 1st∼5th switches 2, 3, 6, 7 and 13 are turned off again. When the 5th switch 13 is turned on by the 3rd clock pulse, the electric charge charged in the stray capacity 3 is discharged through the 5th switch 13. The switch configuration repeated with the switching control cycle at a prescribed period acts like a cosine filter. Thus, the effect on the gain due to the stray capacitance is avoided.