To provide a gas liquefaction device and a gas liquefaction method employing said gas liquefaction device, capable of supplying high-pressure natural gas in a device which liquefies a feed gas with a high efficiency by utilizing the coldness of liquefied natural gas. This gas liquefaction device comprises a main heat exchanger (2) which cools feed gas that has been compressed by a first compressor (1), a first pressure reducing valve (3) which decompresses and cools the feed gas, a gas-liquid separator (4) which subjects the feed gas that has been discharged from the first pressure reducing valve (3) to gas-liquid separation, a first pump (11) which pressurises the liquefied natural gas to a first pressure, and a second pump (12) which pressurises the liquefied natural gas to a second pressure higher than the first pressure, wherein, in the main heat exchanger (2), heat is exchanged between the feed gas on the one hand, and the liquefied natural gas pressurised by the first pump (11) and the liquefied natural gas pressurised by the second pump (12) on the other hand.
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