An oxygen concentrating apparatus 10 for generating oxygen enriched gas by adsorbing and separating nitrogen gas from air, comprises; an oxygen concentrator 40 having an adsorption cylinder filled with adsorbent for adsorbing nitrogen gas, also having an air inlet port 44, an oxygen outlet port 50 and a nitrogen gas outlet port 46; a compressor 30 for supplying compressed air from the air inlet port 44; a sound insulation box 20, which surrounds the compressor 30, for reducing noise generated from the compressor 30, ribs 20a being formed on a side wall of the sound insulation box 20; a cooling fan 36 for introducing air into the sound insulation box 20 so as to cool the compressor 30 by the introduced air; a housing 12 surrounding the oxygen concentrator 40 and the sound insulation box 20; and an exhaust duct 60 arranged in the housing 12, for guiding the exhaust discharged from the cooling fan 36 to the outside of the housing 12.