NOVELTY - A raw biogas (202) and basic aqueous solution (208,214) is injected into absorption column under conditions to permit solubilization of aqueous-soluble biogas components in the basic aqueous solution, to obtain methane-enriched biogas and basic aqueous solution. The methane-enriched biogas and solution comprising aqueous-soluble biogas components are collected. The basic aqueous solution comprising aqueous-soluble biogas components is subjected to treatment for removal of biogas components, to obtain basic aqueous solution. Thus, the methane-enriched biogas is manufactured.    USE - Manufacture of methane-enriched biogas used as fuel for generating engine.    ADVANTAGE - The method is environmental-friendly and efficiently provides methane with high purity and excellent productivity.    DETAILED DESCRIPTION - A raw biogas and basic aqueous solution is injected into absorption column under conditions to permit solubilization of aqueous-soluble biogas components in the basic aqueous solution, to obtain methane-enriched biogas and basic aqueous solution comprising aqueous-soluble biogas components. The methane-enriched biogas and basic aqueous solution comprising aqueous-soluble biogas components are collected. The basic aqueous solution comprising aqueous-soluble biogas components is subjected to treatment for removal of aqueous-soluble biogas components, to obtain basic aqueous solution. A portion of obtained basic aqueous solution is injected into absorption column and the other portion is subjected to biological purification process, to obtain a purified basic aqueous solution. The purified basic aqueous solution is injected into absorption column. Thus, the methane-enriched biogas is manufactured. The basic aqueous solution comprises sodium hydroxide. The gasified components are subjected to absorption column(s) comprising non-organic absorption solution to obtain purified carbon dioxide and absorbed non-organic components containing hydrogen sulfide or ferric chloride. An INDEPENDENT CLAIM is included for production apparatus of methane-enriched biogas.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the production apparatus of methane-enriched biogas.    Production apparatus of methane-enriched biogas (200)    Raw biogas (202)    Basic aqueous solution (208,214)    Pressure release column (232)    Collecting vessel (252)