PURPOSE: To quickly return to an air-fuel ratio at the time of shifting from a decelerating or on-highland operation to a stationary or accelerating operation, by making the lower limit of a compensation coefficient equal to a normal value when a demanded injection quantity is larger than a minimum injection quantity and by making said lower limit higher than the normal value when the demanded injection quantity is smaller than the minimum injection quantity.

CONSTITUTION: When an exact feedback compensation is performed as a calculated demanded injection quantity Qa is larger than a minimum injection quantity Qb determined by the minimum valve opening time of an injector 26, a normal value D is applied as the lower limit FAFmin of an air-fuel feedback compensation coefficient. When the exact feedback compensation is not performed, a value E higher than the normal value D is applied as the lower limit FAFmin of the compensation coefficient. The air- fuel ratio feedback compensation coefficient FAF is guarded by the lower limit FAFmin to complete a routine. Since the air-fuel ratio feedback compensation coefficient is thus guarded in a decelerating operation by the lower limit higher than the normal value, the compensation coefficient is quickly returned to a control region when a stationary operation is resumed.