To secure flow rate measuring accuracy of an air flow meter in an internal combustion engine with a supercharger for returning blow-by gas to an intake passage on the upstream side of the supercharger.

A mesh net 8 for gathering oil mist is arranged in the intake passage 21 between the air flow meter 4 and a return port 71 of a blow-by gas passage 7 to the intake passage 21. By providing the mesh net 8, the blow-by gas existing near the supercharger 5 is heated by the supercharger 5 during stopping of the engine, the oil mist M can be gathered by the mesh net 8 before the air flow meter 4 even when an oil component in the blow-by gas is expanded like the mist, and deterioration of measuring accuracy caused by adhesion of the oil to the air flow meter 4 can be suppressed.