To provide a gas refinery for producing high-concentration methane in high recovery while cutting operating power and cutting greenhouse gases.

The gas refinery works as follows: a gas comprising methane and carbon dioxide is scrubbed at ordinary pressure by a scrubbing means 4 to dissolve the carbon dioxide into the scrubbing water without using any pressurizing power to obtain an about 90%-methane-containing gas; the moisture in the resultant gas is removed by a relevant means 8; the humidity of the moisture-removed gas is reduced by a relevant means 9; the resultant gas is introduced into a separation membrane 10 where the gas is separated into a methane-based refined gas and an off-gas without causing cloggings as a result of dew condensation; thereafter, using low operating power for compression needed in making a membrane separation such as using a compressor 5, the methane concentration raised to about 90% by the scrubbing means 4 is further raised to about 98%; the off-gas is returned via an off-gas-returning line L1 by the scrubbing means 4 or to an upstream side of the means 4; thus methane recovery is raised to about 95% to cut greenhouse gases.

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