An air flow measuring device has a throttle portion provided in a first sub-passage, a second sub-passage branched from the first sub-passage at an upstream side of the throttle portion, and a flow amount sensor located in the second sub-passage. The second sub-passage is configured to introduce therein a part of air flowing in the first sub-passage, and an inlet of the second sub-passage is open into the first sub-passage at one side in a first radial direction perpendicular to a flow direction of air flowing in the first sub-passage. Furthermore, the throttle portion is provided to gradually reduce a passage dimension of the first sub-passage in a second radial direction, as toward an outlet of the first sub-passage. Here, the second radial direction is perpendicular to a surface defined by the first radial direction and the flow direction of air in the first sub-passage.