PURPOSE: To prevent the overrich of air-fuel ratio due to air suction delay upon acceleration by comparing the computed value of the fuel injection quantity with a preset reference value to correct the former value when the rotational speed of an engine after starting the acceleration exceeds a predetermined value.

CONSTITUTION: An fuel injection quantity control circuit 14 takes in the driving condition of an engine, and computes the necessary fuel injection quantity by a control program to control an injector 20. The reference value of the predetermined fuel injection quantity is accommodated in the control circuit 14 so that the air-fuel ratio becomes richer than the theoretical air-fuel ratio in the initial period of the acceleration. In a case where the rotational speed of the engine after the starting of the acceleration is more than the predetermined value, the above reference value is compared with the computed value. When the computed value exceeds the reference value, the fuel injection quantity is controlled on the basis of the reference value.