To improve durability of an air cleaner and miniaturize it by restraining the suction of a dust to the air cleaner by restraining the blow up of the dust on the road surface by the cooling wind, exhausted from the exhaust wind port of the shroud of a forced-air cooled internal combustion engine mounted on a vehicle.

This forced air-cooled type internal combustion engine 3 mounted on a vehicle is provided with a cooling fan 16, a cylinder 10, having a cooling fin 25 and a shroud surrounding the cylinder 10 for forming the passage of a cooling wind from the cooling fan 16 in a space toward the cylinder 10. An exhaust wind guide 30, with which the direction of the flow of the cooling wind at the exhaust wind port 32 becomes nearly parallel with a horizontal surface (road surface), is provided on the part facing to the road surface of the shrouds 15U, 15L.