PURPOSE: To attain the reduction in the circuit scale, the simplicity in the signal switching, high speed in the D-A mode and the extension of the dynamic range by providing a changeover switch switching an analog input signal and a prescribed DC voltage and sampling the analog input signal in the A-D mode and sampling a prescribed DC voltage in the D-A mode respectively.

CONSTITUTION: A changeover switch S4 switching the analog input signal and a prescribed DC voltage Vs is provided and the analog input signal at the A-D conversion is supplied to a capacitor 22 via the changeover switch S4 and a sampling switch S1. Then the prescribed DC voltage is fed to the capacitor 22 at the D-A conversion through the changeover switch and the sampling switch. Thus, in the discharge period of the D-A mode, since the capacitor 22 is charged by an output current of an operational amplifier 11, high speed is attained. Moreover, in the D-A mode, the optional DC voltage Vs is sampled to obtain a desired discharge reset level, the dynamic range of the output of the integration device 20 is expanded.