An air flow measuring device to be installed in an air intake passage of an internal combustion engine with a flange such that one end portion of the air flow measuring device is arranged in the air intake passage through which a main air flow flows, wherein the air flow measuring device has: - a flow measuring element, - an electronic circuit, and - a housing which forms a sub-passage, said housing has an upstream side and a downstream side opposite to the upstream side; wherein said sub-passage comprises: - an inlet opened at an upstream side of said housing, perpendicular to the main air flow, - an air vent disposed at a downstream side of said housing with respect to the inlet and communicating with the air intake passage, - an outlet towards the intake passage, - a first vertical path communicating with said inlet, the first vertical path being provided with said air vent and having a passage portion substantially parallel with a direction of the main air flow and a passage portion with an inclination at the base of which said air vent is provided, wherein said sub-passage is disposed in said one end portion of the air flow measuring device to conduct a part of the air flow flowing through the air intake passage, and wherein a flow measuring element is arranged in the sub-passage to measure the air flow, wherein the sub-passage comprises: - a branching path (74, 75) branching off from the first vertical path towards the flange with a bend portion (8, 75) in a wall of the branching path (74, 75) at the passage portion substantially parallel with the direction of the main air flow of the intake passage between the inlet and the air vent, and upstream of the inclination, characterized in that the branching path (74, 75) is configured to take a part of the air flowing through the first vertical path substantially parallel with the air flow of the main intake passage, wherein the flow measuring element is arranged in the portion of said branching path (74,75), where the direction of air flow is parallel to the direction of the air flow in the intake passage, and wherein the outlet is provided at the end of the branching path (74, 75) and has an opening face parallel to the air flow in the air intake passage. - a flow measuring element, - an electronic circuit, and - a housing which forms a sub-passage, said housing has an upstream side and a downstream side opposite to the upstream side; wherein said sub-passage comprises: - an inlet opened at an upstream side of said housing, perpendicular to the main air flow, - an air vent disposed at a downstream side of said housing with respect to the inlet and communicating with the air intake passage, - an outlet towards the intake passage, - a first vertical path communicating with said inlet, the first vertical path being provided with said air vent and having a passage portion substantially parallel with a direction of the main air flow and a passage portion with an inclination at the base of which said air vent is provided, - a branching path (74, 75) branching off from the first vertical path towards the flange with a bend portion (8, 75) in a wall of the branching path (74, 75) at the passage portion substantially parallel with the direction of the main air flow of the intake passage between the inlet and the air vent, and upstream of the inclination,