NOVELTY - A denitrifying method of organic natural water involves nitrous acid type nitrification process which introduces organic natural water (10) containing ammonia nitrogen into sub-nitrification tank (2) and oxidizes to nitrite nitrogen by action of ammonium oxidizing bacteria, denitrifying process which introduces effluent from sub-nitrification tank into denitrifying tank and generates nitrogen gas by action of denitrifying bacteria, and biological oxygen demand (BOD) decomposition process which introduces organic matter into BOD decomposition tank (1) and decomposes organic matter.    USE - A denitrifying method of organic natural water.    ADVANTAGE - The method prevents generation of nitrogen gas and dinitrogen monoxide in sub-nitrification tank.    DETAILED DESCRIPTION - A denitrifying method of organic natural water involves injecting raw food carrier (8, 9) in organic waste water which contains ammonia nitrogen in front stage of nitrous acid type nitrification process, carrying out nitrous acid type nitrification process which introduces organic natural water (10) containing ammonia nitrogen into sub-nitrification tank (2) and oxidizes to nitrite nitrogen by action of ammonium oxidizing bacteria, performing denitrifying process which introduces effluent from sub-nitrification tank into denitrifying tank and generates nitrogen gas by action of denitrifying bacteria, and carrying out biological oxygen demand (BOD) decomposition process which introduces organic matter into BOD decomposition tank (1) and decomposes organic matter. The amount of aeration is controlled in BOD decomposition tank so that amount of dissolved oxygen is less than or equal to 2.8 mg/L.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of apparatus for denitrifying method of organic natural water. (Drawing includes non-English language text).    Biological oxygen demand decomposition tank (1)    Sub-nitrification tank (2)    Anaerobic ammonia oxidation reaction tank (3)    Raw food carrier (8, 9)    Organic natural water (10)