A/D CONVERTER

PURPOSE:To remove the influence of a leak current by driving the switch on the integration circuit side of a switched capacitor at a specific period. CONSTITUTION:A voltage input circuit 11 including a switched capacitor circuit 22 and a reference charge and bias charge injecting circuit 12' including a switched capacitor circuit 24' are provided on the input side of the integration circuit 13 of a changed balanced type A/D converter, and switches Si3 and Sr3 connected in the switched capacitor circuits 22 and 24' on the sides of the integration circuit 13 are oscillated by a switch control circuit 15 at a specific period. Consequently, the relatively simple constitution converts a signal voltage Vi, reference voltage Vr, and bias voltage Vb into charges, which are injected into the integration circuit 13 to prevent a leak current from exerting influence upon a gain as an error.