To provide an apparatus for processing evaporated gas of liquefied natural gas capable of being compressed down to a liquefied temperature by a less amount of driving power and being liquefied again. ! This processing apparatus is comprised of a cold heat accumulating tank 13 having, as its cold heat accumulating agent, n-butane for use in accumulating cold heat of liquefied natural gas; an evaporated gas compressor 26 for pressurizing and compressing evaporated gas; and a heat exchanger 14 arranged in the cold heat accumulating tank 13 for heat exchanging between the compressed evaporating gas and cold heat accumulating agent in a cold heat accumulating tank 13 and re-liquefying it. Then, n-butane is used as the cold heat accumulating agent to enable the evaporating gas to be liquefied with a liquefying pressure of the evaporating gas at 0.6 to 0.7 MPa, to reduce a driving power for the evaporated gas compressor 26 and perform a reliquefying state in an efficient manner. ! (C)2002,JPO