The purpose of the present invention is to improve cooling efficiency of a cylinder head of an air-cooled engine.With regard to the construction that a cooling fan is provided at one of ends of a crankshaft, and cooling air from the cooling fan is guided to a cylinder head 4 so as to cool the cylinder head 4, an intake manifold 8 is arranged above the cooling fan, a duct 51 is provided at the lateral center of the intake manifold 8 so as to suck air from an air cleaner, cooling air is sent from both sides of the duct 51 to an intake valve, an exhaust valve and an injection nozzle arranged in the cylinder head 4, and a shielding plate 55 is provided at one of lateral sides of the duct 51.