A gas liquefaction apparatus includes at least a source-gas supply line that supplies source gas; a room-temperature heat exchanger, a preliminary-cooling heat exchanger, and a liquefaction/supercooling heat exchanger that are provided in series sequentially in the source-gas supply line and that cool the source gas; a separation drum that separates the source gas containing a condensate, which has been cooled by heat exchange up to a liquefaction temperature of the source gas or below, into a gas component and a liquefied component; and a refrigerant-gas supply line that uses a gas component separated by the separation drum as refrigerant gas to supply the refrigerant gas in a direction opposite to a supply direction of the source gas, in order of the liquefaction/supercooling heat exchanger, the preliminary-cooling heat exchanger, and the room-temperature heat exchanger.