Abstract: An air meter for an internal combustion engine. The air intake passage of the internal combustion engine includes a main passage and an L-shaped auxiliary passage. The auxiliary passage includes a first flow passage, a second flow passage and a corner portion arrnaged at a corner thereof. The first flow passage communicates to the second flow passage through the corner portion. The first flow passage is disposed in parallel with the main passage and has a hot wire sensor arranged therein. The second flow passage is arranged perpendicularly to the main passage. The first flow passage has a circular radial cross section. The second flow passage is in the shape of a groove with a bottom, the groove having a square cross-section. The first flow passage is open to the corner portion at a level of the bottom of the second flow passage.