PURPOSE: To prevent the generation of noise of a heat resistor type airflow meter output by setting the cut-off frequency of a low-pass filter circuit for an airflow meter to specified value.

CONSTITUTION: An intake air amount detecting device for an engine is formed such that a base plate is disposed in a direction crossing the direction of a flow of intake air in an intake pass approximately at right angles and a heat resistor is securely formed to the surface, situated upper stream of intake air, of the base plate. The cut-off frequency of a low-pass filter circuit 38 for the airflow meter 1 is set to 120Hz or less.