NOVELTY - The gas discharged by refiner (65) is passed into a lower section of dilution tanks (10A,10B) containing primary raw material (M1). The discharged gas is oriented to the bottom surface (10a) of the dilution tanks. Nitrogen and oxygen mixed in the primary raw material of dilution tank after gas discharge process, are set in the top surface of the primary raw material. The storage gas stored in upper section of dilution tanks is absorbed by a suction pump (P2).    USE - Generation method of biogas for fuel cell and power generation equipment.    ADVANTAGE - The biogas generation process can be performed at reduced co st, by methane-fermenting from organic waste. The deaeration of nitrogen and oxygen in biogas generation system can be performed effectively. The raw material supply process can be performed effectively without interruption by the supply of deaerated nitrogen and oxygen.    DETAILED DESCRIPTION - The storage gas suction process is implemented over one cycle until the passage of organic waste and water into the dilution tank. The gas discharge process is implemented after stirring organic waste and water. An INDEPENDENT CLAIM is included for biogas generation system (1), which comprises a fermenter (50) that generates fermentation gas by methane fermentation within dilution tanks after mixing of organic waste and water. Unnecessary gas in fermentation gas is removed to generate biogas. The gas discharged from annular or plate shaped gas discharge unit (20) of refiner is passed to liquid level of raw material through a nozzle from dilution tanks. The atmosphere of space on the top surface of raw material of dilution tanks is absorbed. Organic waste and water stirring unit is extended on diameter outer side focusing on hollow-shaped axial portion extended in axial direction of dilution tank. Gas discharge unit is connected to axial portion pipeline provided in blade having smaller diameter than that of dilution tanks. The dilution tanks are arranged in parallel by the side of fermenter. Gas discharged from refiner is passed through gas pipe line connected in parallel with gas discharge portion of dilution tanks.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view illustrating the structure of biogas generation system. (Drawing includes non-English language text)    Biogas generation system (1)    Dilution tanks (10A,10B)    Bottom surface of dilution tanks (10a)    Gas discharge unit (20)    Fermenter (50)    Refiner (65)    Primary raw material (M1)    Suction pump (P2)