PURPOSE: To control air-fuel ratio in transient state properly and prevent an engine from stopping and so on by correcting detected value of intake air volume in depending on opening of a throttle valve and condition of transient state.

CONSTITUTION: Signals from a crank angle sensor 9, an air flow meter 2 and a throttle sensor 3 and so on are put in to a control unit 10 for operating fuel injecting quantity based on intake air volume and engine speed. In this case, intake air volume signal is corrected based on fixed operation expressions with using opening of the throttle valve and rate of change of intake air volume. Thereby, generation of hesitation due to too rich air-fuel ratio in a case of acceleration or engine stop due to too lean in a case of deceleration can be prevented.