An air flow measuring device includes a fitted part, a housing, a flow sensor, and a temperature sensor component. A projection shape of the fitted part onto an imaginary plane is a first circle. On the imaginary plane, a first point and a second point are located on the first circle or inward of the first circle, and a third point is located inward of the first circle. A diameter of an imaginary circle passing through the first, second, and third points is larger than a diameter of the first circle. The first, second, and third points have such a positional relationship that, when at least one of the first and second points comes into contact with an inner peripheral surface of an attachment hole at time of insertion of the housing into a duct, the third point is away from the inner peripheral surface of the attachment hole.