PURPOSE: To restrict the deterioration of the exhausting performance by providing an additional charge time correction value presuming means for estimating the correction value of the air-fuel ratio controlled variable on the basis of a result of estimation of a purge gas concentration change presuming means.

CONSTITUTION: In an exhaust passage 6, an air-fuel ratio sensor 7, which detects the concentration of the oxygen contained in the exhaust so as to detect the air-fuel ratio of the intake mixture, is provided in a manifold collecting part. A control unit 10 computes the fuel quantity corresponding to the target air-fuel ratio on the basis of values detected by various sensors. The injection pulse signal having a pulse width corresponding to this fuel quantity is output to a fuel injection valve 14. In the case there is the additional charge, since the quantity of displacement of the air-fuel ratio feedback correction coefficient can be estimated in response to that additional charge, even in the case there is the additional charge, the device can accurately cope with a stage difference of the air-fuel ratio, which is generated with a start of purge processing, with the excellent responsiveness. Deterioration of the exhausting performance can be thereby effectively restricted.