There is provided an air flow meter (7) for detecting the flow rate of air, an electronically controlled throttle (13) for opening and closing a throttle valve and a calculating device (14, 801) to which a target engine intake air flow rate, a value detected by the air flow meter, the position of a throttle valve detected by a throttle position sensor, and a value detected by an engine speed sensor are input. The calculating device calculates a time constant of a delay of response of the air flow rate into the engine, and an air flow rate passing through the throttle valve to compensate for the delay of response, and drives the throttle valve such that the flow rate of air passing through the throttle valve agrees with the calculated value.