PURPOSE: To prevent fluctuation in an air fuel ratio, and to improve control accuracy by adding another function for connecting two first order lag element of different time constants, together in parallel, so as to calculate a new correction coefficient, to a control part, and whereby correcting the fluctuation in the air fuel ratio at the time of acceleration or deceleration, through the correction coefficient.

CONSTITUTION: The amount of fuel injection from an injector 18 is changed according to the amount of intake air, and fluctuation in an air fuel ratio is corrected and controlled by a control part (ECM) 34. An oxygen sensor 16, the injector 18, a fuel pump 24, a pressure regulator 26, an inlet-air temperature sensor 28, a pressure sensor 30, and a throttle position 32 are connected to the ECM 34. A function is added to the ECM 34, in which two first order lag elements of different time constants are connected together in parallel, to calculate a new correction coefficient, and the fluctuation in the air fuel ratio at the tine of acceleration or deceleration is corrected by the correction coefficient. Good control accuracy of the air fuel ratio at the time of acceleration and deceleration can thus be achieved, while reliability of control can be improved.