An air flow measuring device includes a housing, a sensor, and a projection portion. The housing defines a bypass flow passage through which taken-in intake air passes and which has an outlet that opens into an intake passage toward a downstream side of a mainstream of intake air. The sensor is accommodated in the bypass flow passage to produce an electrical signal as a result of heat transfer between the taken-in intake air and the sensor. The projection portion is provided on an outer wall of the housing on a downstream side of the outlet in the mainstream and extends outward of the housing. A projection-portion projected region and an outlet projected region, which are formed respectively by projecting the projection portion and the outlet perpendicularly onto a projection plane that is perpendicular to a direction of the mainstream, overlap with each other.