NOVELTY - Hydrogen is isolated from production gas using membrane separator (5). Carbon monoxide and methane gas from membrane separator is fed to abdominal portion of methane gas absorption tower (7), when lean oil (18) is fed to tower top. Lean oil is fed from bottom portion of absorption tower to lean oil regeneration tower (8). Circulation supply of tower bottom liquid of regeneration tower is carried out to tower top of absorption tower.    USE - For separating and recovering carbon monoxide from production gas of petroleum-refinery hydrogen-production apparatus.    ADVANTAGE - The carbon monoxide byproduced is the reformer is converted to carbon dioxide with desulfuring apparatus catalyst. Methane gas of high purity is effectively and efficiently recovered.    DETAILED DESCRIPTION - Hydrogen is isolated from production gas of reformer of petroleum-refinery hydrogen-production apparatus, using a membrane separator having a hydrogen permeable film. The carbon monoxide and methane gas from the membrane separator is supplied to the abdominal portion of methane gas absorption tower used as upstream distilling column, when lean oil is supplied to the tower top of the absorption tower. Methane gas is absorbed, and high concentration oxidation oxygen is recovered from exhaustion portion of the absorption tower. The lean oil is supplied from bottom portion of the absorption tower to lean oil regeneration tower used as downstream distilling column. Methane gas is evaporated and exhaust gas recovery is carried out. Circulation supply of the tower bottom liquid (lean oil) of lean oil regeneration tower is carried out to tower top of absorption tower. Thus, separation and recovery of carbon monoxide from production gas of petroleum-refinery hydrogen-production apparatus is enabled.    DESCRIPTION OF DRAWING(S) - The figure shows the explanatory drawing illustrating the gas treatment process flow of hydrogen gas/methane gas/carbon monoxide gas separation apparatus. (Drawing includes non-English language text).    waste-heat turbine generator (2)    cooler (3)    membrane separator (5)    methane gas absorption tower (7)    lean oil regeneration tower (8)    lean oil (18)