A car exhaust gas purification device controlling circuit wherein a deviation between an output of an exhaust gas sensor and a set value is converted into a time-width signal and a proportional electromagnetic valve is controlled by an integrated output of the time-width signal to control the air-fuel ratio around a theoretical air-fuel ratio, whereby an offset of air-fuel ratio due to hysteresis of such as the proportional electromagnetic valve used for controlling the air-fuel ratio is eliminated.