PURPOSE: To facilitate compensating pressure of a vortex flow meter, by providing a pressure detecting means for detecting the pressure on the upstream side of a vortex flow meter for detecting the flow rate of intake air, and controlling the valve driving duration of a fuel injecting solenoid valve in response to the output of the pressure detecting means.

CONSTITUTION: When an engine is set into operation, intake air is introduced from an inlet pipe 10 and carried via an air cleaner 8 into a vortex flow meter 4, by which the flow rate of intake air is detected. Then, the intake air is introduced into an intake pipe 2. Here, as the flow rate of intake air is increased, pressure of intake air passed through the vortex flow meter 4 is dropped by the resistance of inlet pipe 10 and air cleaner 8. This pressure drop is detected by a pressure detecting means 7 and the output signal of the means 7 is given to an electronic control means 6 for preventing the mixture from becoming too rich by compensating the valve driving duration of a fuel injection solenoid valve 5 by the electronic control means 6 in response to the output signal of the pressure detecting means 7.