PURPOSE: To accurately detect air flow by providing a first lead part for supplying resistance part with a current and a second lead part for measuring the voltage at the resistance part.

CONSTITUTION: The device is constituted of a body 1 and a module 2. The suction air is separated into a main flow path 3 and a subflow path 4. A heating resistor 5 and a temperature sensing resistor 6 are welded to a support pin and arranged in the subflow path 4. To a heating resistor 5 arranged in the subflow path 4, a current for heating to a constant temperature is impressed. The heated temperature is kept so that the temperature difference between the heating resistor 5 and the air is constant regardless of the suction air flow and the air temperature is corrected with a temperature sensing resistor 6. Two lead wires 8 are withdrawn out of both ends of heating resistor 5 and the temperature sensing resistor 6, respectively and are electrically connected with conductive bond 9 inside a ceramic bobbin 11. To the lead wires 8, a resistor 10 is connected, covered with a clad 12 and they constitute the heating resistor 5 and the temperature sensing resistor 6 having a four terminal structure.