Muffler connected to the exhaust-discharging end of an engine is positioned above the engine adjacent a fuel tank. Heat blocking cover covers top and side portions of the muffler, and a fan cover, generally in the shape of a cylinder and extending close to the engine, covers an electric-power generator. Cooling fan device is provided in a cooling-air inlet portion of the fan cover for introducing cooling air from the outside to the electric-power generator covered with the fan cover. Engine-cooling air passage having a cooling-air inlet portion that faces a cooling-air outlet portion of the fan cover is provided to cool an outer surface of the engine by the cooling air flowing out through the cooling-air outlet portion of the fan cover. The engine-cooling air passage is branched upward to provide a separate muffler-cooling air passage extending between the muffler and the heat blocking cover above the engine. Thus, the cooling air introduced from the outside is allowed to cool both the engine and the muffler after having cooled the electric-power generator. With such arrangements, the engine, generator and muffler can be cooled with enhanced efficiency in a very simple manner.