To perform with high accuracy the analog-to-digital conversion of signals of an air flow meter irrespective of fluctuation of a reference voltage of an analog-to-digital conversion circuit. A thermal type air flow meter including means for measuring an intake air flow rate by heating and controlling a heating resistor and means for performing analog-to-digital conversion of an air flow rate signal of the air flow rate measurement means, which inputs a reference voltage to the analog-to-digital conversion circuit so that the reference voltage can be converted from the analog signal to the digital signal by the analog-to-digital conversion circuit, and the air flow rate signal can be corrected in accordance with the value of the reference voltage. A/D conversion of the air flow rate signal can be executed accurately even when the voltage of the reference voltage source of the A/D converter in an electrical control unit is fluctuating.