NOVELTY - Sulfur-type impurity and carbon dioxide are separated from biogas, and high concentration methane gas is purified. Hydrogen is added to purified gas, and gas is filled in deoxidation catalyst tower. Oxygen remained in purified gas is converted to water. The flow volume of purified gas supplied to catalyst tower is measured. The oxygen concentration in the purified gas supplied to deoxidation catalyst tower, and oxygen concentration in purified gas after passing through the tower are measured. Thus, deoxidization of biogas is enabled.    USE - Deoxidization of biogas.    ADVANTAGE - The amount of hydrogen added to biogas is efficiently controlled, and deoxidization of biogas is stably carried out.    DETAILED DESCRIPTION - Sulfur-type impurity and carbon dioxide are separated from biogas, and high concentration methane gas is purified by physical-absorption method using water as a solvent. Hydrogen is added to purified gas containing argon, and gas is filled in deoxidation catalyst tower containing catalyst. Oxygen remained in purified gas is converted to water by catalytic reaction. The flow volume of purified gas supplied to catalyst tower is measured. The oxygen concentration in the purified gas supplied to deoxidation catalyst tower, and oxygen concentration in purified gas after passing through the tower are measured by electrochemical method using an electrode system. The amount of hydrogen added to purified gas during hydrogenation is adjusted based on measured oxygen concentration and flow volume of purified gas. Thus, deoxidization of biogas is enabled. An INDEPENDENT CLAIM is included for deactivator of biogas, which has a biogas purifier (2) for separating sulfur-type impurity and carbon dioxide from biogas, hydrogen supply unit (13) for adding hydrogen to purified gas, deoxidation catalyst tower (20), a flow measurement unit (11), electrochemical-type oxygen concentration measurement unit (40), and amount adjustment means of hydrogen for adjusting hydrogen amount based on the flow volume of purified gas.    DESCRIPTION OF DRAWING(S) - The drawing shows the explanatory view of deactivator of biogas. (Drawing includes non-English language text)    Biogas purifier (2)    Flow meter (11)    Hydrogen supply unit (13)    Deoxidation catalyst tower (20)    Oxygen concentration measurement unit (40)