NOVELTY - A nitrogen component contained in raw material is converted into ammonia using ammonia fermented before sending raw material of organic waste for methane gas generation into methane fermentation tank (7). The ammonia content in raw material to which ammonia conversion process is carried out is removed by gasification while introducing raw material into closed circulatory system ammonia removal equipment (3) and then circulated under anaerobic atmosphere. Then, raw material is sent to methane fermentation tank and some raw materials in methane fermentation tank are extracted.    USE - Removal of ammonia during formation of methane.    ADVANTAGE - The method economically removes ammonia during methane formation with high removal efficiency.    DETAILED DESCRIPTION - A nitrogen component contained in raw material is converted into ammonia using ammonia fermented before sending the raw material of organic waste for methane gas generation into methane fermentation tank. The ammonia content in the raw material to which ammonia conversion process is carried out is removed by gasification while introducing raw material into closed circulatory system ammonia removal equipment (3) and then circulated under anaerobic atmosphere. Then, the raw material is sent to methane fermentation tank and some raw materials in the methane fermentation tank are extracted in closed circulatory system ammonia removal equipment (10) in parallel to methane fermentation process. The ammonia contained in the raw material is subjected to gasification removal while circulating the raw material in the apparatus under anaerobic atmosphere, the mixture is returned to methane fermentation tank and ammonia is removed. An INDEPENDENT CLAIM is included for ammonia removal system.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic structure of ammonia removal system. (Drawing includes non-English language text)    Ammonia fermenter (2)    Closed circulatory system ammonia removal equipments (3,10)    Methane fermentation tank (7)    Heater (8)    Heat-exchanger (9)