NOVELTY - Sewage gas having increased pressure and absorption water having increased pressure are contacted in absorption tower (404). Carbon dioxide of sewage gas is dissolved in water, and is separated. Absorption water is discharged out of system, when feed water temperature is low. Absorption water having carbon dioxide is fed into desorption tower, when feed temperature is high. Dissolved carbon dioxide is removed, and pressure of regenerated water is increased and cooled. The resulting water is supplied to absorption tower. Thus, purification of sewage gas is enabled.    USE - Purification of sewage gas and producing fuel.    ADVANTAGE - The sewage gas is economically purified. The concentration of methane in purified gas is uniformly maintained.    DETAILED DESCRIPTION - Sewage gas having increased pressure and absorption water having increased pressure are contacted in an absorption tower (404). The sewage gas is produced by heating and carrying out anaerobic fermentation of organic substance in digester. Carbon dioxide of sewage gas is dissolved in absorption water, and is separated to obtain purified gas having highly concentrated methane. The absorption water ejected from absorption tower is temporarily discharged out of the system, when the feed water temperature is low. The absorption water containing carbon dioxide in dissolved state is introduced into desorption tower, when feed water temperature is high. The dissolved carbon dioxide is removed, and the pressure of obtained regenerated water is further increased and cooled. The resulting water is switched to circulation mode, and supplied to absorption tower. Thus, purification of sewage gas is enabled. An INDEPENDENT CLAIM is included for sewage gas refiner.    DESCRIPTION OF DRAWING(S) - The drawing shows the flowchart illustrating sewage gas purification method. (Drawing includes non-English language text)    Sewage gas refiner (4)    Mist separator (401)    Gas compression machines (402a,402b)    Absorption tower (404)    Dehumidifier (405)