NOVELTY - A rough oxygen concentration is generated using oxygen as a raw material by distillation apparatus (11). The obtained rough oxygen concentration is added to hydrogen, to obtain water. The nitrogen monoxide is generated using nitrogen monoxide as a raw material by distillation apparatus (12). The obtained water and the nitrogen monoxide are chemically exchanged, to obtain nitrogen monoxide having increased concentration of oxygen isotopes, and water having reduced concentration of oxygen isotopes. Thus, the concentration of oxygen isotope is performed.    USE - Concentration method of oxygen isotope (claimed).    ADVANTAGE - The method enables concentration of oxygen isotope without requiring regular replenishment of the nitric oxide starting material in large amounts and without reducing the separation efficiency of oxygen isotopes, and with small amount of liquid nitrogen oxide hold-up.    DETAILED DESCRIPTION - A rough oxygen concentration is generated using oxygen as a raw material by distillation apparatus. The obtained rough oxygen concentration is added to hydrogen, to obtain water. The nitrogen monoxide is generated using nitrogen monoxide as a raw material by distillation apparatus. The obtained water and the nitrogen monoxide are chemically exchanged, to obtain nitrogen monoxide having increased concentration of oxygen isotopes, and water having reduced concentration of oxygen isotopes. The nitrogen monoxide having increased concentration of oxygen isotopes is sent to the distillation apparatus (12), and water having reduced concentration of oxygen isotopes is electrolyzed and sent to the distillation device (11). Thus, the concentration of oxygen isotope is performed.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart explaining the concentration method of oxygen isotope. (Drawing includes non-English language text)    Oxygen isotopic enrichment apparatus (10,100)    Distillation apparatus (11,101)    Distillation apparatus (12)    Hydrogenation potion (14)    Chemical replacement tower (16)