PURPOSE: To improve emission of exhaust gas, by a method wherein, when a feedback correction factor based on an air-fuel ratio detected by an air-fuel ratio detecting means is set to a starting initial value during the starting of deceleration acceleration, a starting initial value is set based on a time average value of a feedback correction factor.

CONSTITUTION: An intake air quantity Qa from a hot wire type airflow meter 9, a throttle opening α from a throttle sensor 10, a cooling water temperature Tw from a water temeprature sensor 11, a crank angle Ca from a crank angle sensor 12, and a detecting signal V from an O2 sensor 13 are inputed to a control unit 21, and feedback control is amde on an opening time of an inejctor 5 so that an air-fuel ratio is adjusted to a target value according to a running state. When, based on the throttle opening α an engine is decided to be in an acceleration or deceleration state, a correcton factor of an air-fuel ratio is initialized by an average time during feedback control.