NOVELTY - A methane fermentation gas containing methane gas and carbon dioxide gas is produced by methane fermentation treatment of organic waste. The obtained methane fermentation gas is purified by performing pressure-swing adsorption process of separating carbon dioxide gas from methane fermentation gas, to obtain methane-enriched gas. Thus, the purification of methane fermentation gas is enabled. The pressure of the methane fermentation gas during purification process is less than the pressure of the methane fermentation gas during production process.    USE - Purification of methane fermentation gas used as town gas material and motor fuel.    ADVANTAGE - The method enables purification of methane fermentation gas with reduced energy.    DETAILED DESCRIPTION - A methane fermentation gas containing methane gas and carbon dioxide gas is produced by methane fermentation treatment of organic waste. The obtained methane fermentation gas is purified by performing at least pressure-swing adsorption process of separating carbon dioxide gas from methane fermentation gas, to obtain methane-enriched gas. Thus, the purification of methane fermentation gas is enabled. The pressure of the methane fermentation gas during purification process is less than the pressure of the methane fermentation gas during production process. The pressure of the purified gas is less than the pressure of the methane fermentation gas. An INDEPENDENT CLAIM is included for purification system (1) of methane fermentation gas, which consists of methane fermentation gas production mechanism and purification mechanism (4) having a purifier which separates carbon dioxide gas from methane fermentation gas by pressure-swing adsorption method.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of purification system of methane fermentation gas. (Drawing includes non-English language text)    Purification system of methane fermentation gas (1)    Methane fermentation processing apparatus (2)    Methane fermentation gas holder (3)    Purification mechanism (4)    Back pressure valve (5)