A sensor assembly includes a sensor portion and a sensor circuit, which are integrated with each other and configured to measure an air flow quantity. A thermistor is configured to measure an air temperature. A metal plate includes a grounding end terminal. One lead wire of the thermistor is joined electrically with the grounding end terminal. The sensor circuit is disposed on the metal plate. The sensor circuit is entirely overlapped with the plate shape portion in a direction perpendicular to the metal plate.