A duct member is disposed around outer peripheries of an engine and an engine-driven generator to define a continuous cooling-air passage between the duct member and the outer peripheries. A cooling fan is disposed in the cooling-air passage to generate a flow of cooling air from one end of the cooling-air passage to the other end during operation of the engine. An intake box is connected to one end of the cooling-air passage and has an air-intake port. A muffler box is connected to the other end of the cooling-air passage, has an air-discharge port, and accommodates an exhaust muffler of the engine. A sound-insulating housing is connected between the intake box and the muffler box to surround the duct member in order to insulate sound emitted from the duct member.