NOVELTY - Sewage gas emitted by carrying out methane fermentation of organic waste is compressed in compressor (2a,2b) and contacted with water in absorption tower (3). The carbon dioxide and sulfur-type impurity in pressurized sewage gas are dissolved in water and separated. Hydrogen sulfide remained in the obtained purified gas is removed in dehumidifier. Hydrogen is added to the dehumidified gas, oxygen in purified gas is converted into water in catalytic tower (8), and hydrogen is supplied. The moisture in purified gas is removed in dehumidifier. Thus, the sewage gas is deoxidized.    USE - Deoxidization of sewage gas.    ADVANTAGE - The sewage gas is efficiently deoxidized using highly-durable catalyst and without requiring high-temperature condition. The deterioration of catalyst by hydrogen sulfide is prevented.    DETAILED DESCRIPTION - Sewage gas emitted by carrying out methane fermentation of organic waste is compressed and pressurized in a compressor, and the pressurized sewage gas is contacted with water in high-pressure state in an absorption tower. The carbon dioxide and sulfur-type impurity contained in the pressurized sewage gas are dissolved in high-pressure water, and the carbon dioxide and sulfur-type impurity are separated from the pressurized sewage gas, to obtain purified methane gas. The purified gas containing hydrogen sulfide is passed to primary dehumidifier, such that hydrogen sulfide with moisture content is removed. Hydrogen is added to the dehumidified-purified gas, oxygen remained in purified gas is converted into water in a catalytic tower filled with catalyst, and hydrogen is supplied according to catalytic reaction. The moisture in purified gas is removed in a secondary dehumidifier. Thus, the sewage gas is deoxidized. An INDEPENDENT CLAIM is included for deactivator, which has compressor, absorption tower, primary dehumidifier, hydrogen supply unit which adds hydrogen to dehumidified purified gas, catalytic tower filled with catalyst, and secondary dehumidifier.    DESCRIPTION OF DRAWING(S) - The drawing shows an explanatory view of deactivator. (Drawing includes non-English language text)    Compressors (2a,2b)    Absorption tower (3)    Catalytic tower (8)    Adsorption towers (9,10)    Gas holder (11)