A detection element portion is provided on an inner surface side of a plate as a wall surface portion defining a measurement passage in a flow measuring device. An intake-air temperature detection portion detecting a temperature of a fluid being measured is provided on one main surface of a substrate forming the detection element portion. A ventilation hole allowing a main passage in which the fluid being measured flows and the measurement passage to communicate is provided so as to penetrate through the plate. By achieving a state in which the substrate forming the detection element portion is installed so that an end thereof protrudes into the ventilation hole and a back surface of the end portion of the detection element portion where the intake-air temperature detection portion is formed is exposed toward the main passage, a response speed is enhanced.