Disclosed is an air cooled internal combustion engine which comprises a cooling fan formed unitarily on a flywheel fixed to one end of an engine crank shaft, a cooling fan case covering the cooling fan and adapted to guide the flow of cooling air generated by the cooling fan toward the engine body, an air cleaner connected to the suction port of the engine, and a silencer connected to the exhaust port of the engine, wherein the suction port is located at the same side of the engine body as the flywheel while the other exhaust port is located at the opposite side of the engine body to the flywheel, and wherein the air cleaner is formed integrally with the cooling fan case.