An intake air amount detecting system which comprises:a temperature-dependent resistor disposed in an intake air path of an internal combustion engine;a sensor control circuit which feeds a heating current to the temperature-dependent resistor, which detects the change in resistance of the temperature-dependent resistor, which amplifies the detected signal, which effects the compensation depending upon the temperature of the intake air, and which controls the heating current in order to maintain the temperature of the temperature-dependent resistor constant; andan operation circuit which converts a signal that represents the heating current into an intake air flow rate;wherein the sensor control circuit is provided with a response-adjusting circuit which delays the response of the heating current only when the intake air flow rate decreases.