NOVELTY - Mixed gas of acidic gas and non-acidic gas, and absorption liquid having ionic liquid are contacted in absorption tower (13). Non-acidic gas is recovered, and acidic gas-absorbed absorption liquid is supplied to regeneration tower (16). Acidic gas is separated and recovered, and absorption liquid is regenerated. Purification of gas is enabled. The ionic liquid is liquid having primary amine group.    USE - For purifying gas ejected from thermal power station, cement plant and chemical processing plant. Also hydrogen separated from gas is used as fuel for fuel battery motor vehicle.    ADVANTAGE - The gas is efficiently and economically purified. The absorbed amount of acidic gas per unit volume of absorption liquid is increased, and circulating load of absorption liquid is decreased.    DETAILED DESCRIPTION - Mixed gas containing acidic gas and non-acidic gas is supplied to lower portion of absorption tower (13). Absorption liquid having ionic liquid is supplied to the upper portion of absorption tower maintained at predetermined temperature and pressure. The mixed gas is contacted with absorption liquid, such that absorption liquid absorbs acidic gas. Non-acidic gas and acidic gas are separated, and non-acidic gas is recovered from absorption tower. The acidic gas-absorbed absorption liquid is supplied to upper portion of regeneration tower (16) maintained at temperature higher than temperature in tower (13), and same or less pressure of tower (13). Acidic gas is dissolved, separated from liquid and recovered from tower (16), and absorption liquid is regenerated. The regenerated absorption liquid is supplied to upper portion of tower (13), and purification of gas is enabled. The ionic liquid is liquid having primary amine group (-NH2). INDEPENDENT CLAIMS are included for the following:    (1) absorption liquid; and    (2) system for supplying hydrogen to hydrogen station. The system carries out modification of fuel chosen from desulfurized gasoline, naphtha, kerosene, methanol, dimethyl ether, liquefied petroleum gas and natural gas, production of mixed gas containing hydrogen and carbon monoxide, modification and removal of carbon monoxide, separation of mixed gas to hydrogen and carbon monoxide, and recovery of hydrogen.    DESCRIPTION OF DRAWING(S) - The figure shows the cross-sectional block diagram of purification method of gas. (Drawing includes non-English language text).    dehumidifier (11)    compressor (12)    absorption tower (13)    regeneration tower (16)    circulating pump (17)