NOVELTY - A biogas purification involves pressure-rising of biogas from anaerobic fermenter which carries out anaerobic fermentation of organic waste by gas-compression machine, contacting biogas and water in high pressure state and sending to absorption tower, dissolving carbon dioxide and sulfur type impurity which are contained in biogas, and isolating impurities from biogas.    USE - Biogas purification for organic waste such as sewage sludge generated in sewage works, and anaerobic digestion such as organic waste water from organic refuse, excrement, livestock, chemical plant and foodstuffs factory.    ADVANTAGE - Installing large sized low pressure gas holder is not necessary, gas pressure of anaerobic fermenter can be maintained to target value with respect to fluctuation of biogas generation amount, and pressure in absorption tower into which biogas is fed can be maintained to setting value.    DETAILED DESCRIPTION - A biogas purification involves:    (A) pressure-rising of biogas from anaerobic fermenter which carries out anaerobic fermentation of organic waste by gas-compression machine;    (B) contacting biogas and water in high pressure state and sending to absorption tower;    (C) dissolving carbon dioxide and sulfur type impurity which are contained in biogas;    (D) isolating impurities from biogas;    (E) inducing purified gas to gas-compression machine by purified-gas circulation line;    (F) running gas-compression machine by predetermined fixed load;    (G) maintaining total amount of purified gas constantly or nearly constantly;    (H) measuring gas pressure of anaerobic fermenter;    (I) increasing or decreasing amount of biogas induced to gas-compression machine so that gas pressure of anaerobic fermenter may be maintained by predetermined target value based on measurement result; and    (J) obtaining gas which is a highly concentrated methane.    An INDEPENDENT CLAIM is included for a biogas refinery processing installation comprising:    (1) gas-pressure meter which measures gas pressure of anaerobic fermenter which carries out anaerobic fermentation of organic waste;    (2) flow-regulation unit for biogas;    (3) biogas leading-out line which induces biogas from anaerobic fermenter;    (4) gas-compression machine which pressure-rising biogas and is run by predetermined fixed load;    (5) absorption tower;    (6) biogas refiner which obtains purified gas;    (7) purified-gas circulation line which induces purified gas to gas-compression machine; and    (8) control unit which increase or decrease amount of biogas induced to gas-compression machine.