PURPOSE: To eliminate effect of intake air pulsation and to perform high-precise computation of an intake air amount by storing an intake air flow rate at a given crank angle during a suction stroke, in order, as a preceding cycle value and calculating a correction value of an intake air flow rate based on the preceding value and a current detected value.

CONSTITUTION: An air cleaner 5, an airflow sensor 6, and throttle valve 7, and an injector 8 are disposed, in the order named, from upstream in the intake air passage 2 of an engine 1. A bypass air valve 11 is disposed to the bypass air passage 10 of the throttle valve 7. The injector 8 is controlled by a controller unit 9 based on various detected signals from various sensors 12-16 to detect the running state of the engine 1. In this case, a correction amount of an intake air amount is calculated based on a preceding cycle value being an intake air flow rate at a given crank angle during a suction stroke and a current detected value. Effect of intake air pulsation is eliminated and high-precise computation of an intake air amount is made.