PURPOSE: To maintain the accuracy of flow rate detection by calculating an average flow rate of the intake air flow rate basing on the adopted detection value as well as by detecting the maximal point of the intake air flow rate variations and selecting the detected value of the intake air flow rate after comparing the maximal point occurring interval time with the standard time.

CONSTITUTION: A temperature sensing type flow meter 1 is impressed with power supply voltage through an ignition switch 2. The output voltage of the temperature sensing type flow meter 1 is inputted into a microcomputer 4 through an A/D transducer 3. Further the detection signal of an engine speed sensor 5 is inputted into the microcomputer 4 which then controls the fuel supply quantity to the internal combustion engine in accordance with each input signal. At this time, the microcomputer 4 calculates an average flow rate of the intake air flow rate basing on the adopted detection value as well as detects the maximal point of the intake air flow rate variations and selects the detected value of the intake air flow rate by comparing the maximal point occurring interval time with the standard time.