A natural gas refining apparatus including a first separation membrane unit including a first separation membrane; and a second separation membrane unit provided in a subsequent stage of the first separation membrane unit. The second separation membrane unit includes a second separation membrane that allows an amine solution to circulate through the second separation membrane unit, and the natural gas refining apparatus refines raw natural gas containing CO2 by passing the raw natural gas through the first and second separation membrane units, separating CO2-rich gas with the first and second separation membranes, and absorbing CO2 with the amine solution circulating through the second separation membrane unit.