The invention relates to a dual-flow turbojet engine comprising an engine which is disposed in a nacelle and is provided with case which defines jointly with the said nacelle an annular passage through which a secondary flow supplied by a fan placed upstream of the engine can flow, a primary nozzle which is fixed to the case downstream of the engine, an internal wall for guiding the main hot flow supplied by the engine and an external wall contacting the secondary flow. Said invention is characterized in that sound attenuating means is provided for at least one part of the internal wall and the external wall is provided with means for cooling said internal wall.