PURPOSE: To get rid of the shortage of output by reducing the proportion constant value and/or integral constant value of a feedback correcting signal which is set based on the set time during acceleration starting and the output signal of an air-fuel ratio.

CONSTITUTION: An air-fuel ratio control means 13 corrects a basic fuel injection quantity obtained in accordance with an operating condition by means of an air-fuel ratio feedback correction factor, etc., to operate an actual fuel injection quantity. In this case, it is judged whether a vehicle is in a started and accelerating condition or not from the output of a throttle position sensor 8 and when a defined time is not elapsed after shifting to the accelerating condition while being judged YES, a starting correction quantity is set to a value smaller than unity (1). Based on the output of an O2 sensor 11, a proportion constant value and an integral constant value which constitute the correction factor are retrieved each from a defined map and these constant values are corrected by the starting correction quantity. The fuel injection quantity is operated based on the corrected air-fuel ratio feedback correction factor.