To reduce the load of a work by heating and vaporizing sampled liquefied natural gas(LNG) at an atmospheric temperature, and analyzing it properly after storing it in a cylinder for a while. ! LNG, flowing in an atmospheric-temperature vaporizing coil part 10 from a sampling nozzle 2, is vaporized at an atmospheric temperature, and the vaporized gas is stored in a cylinder 6 for a while, and thereafter analyzed properly. In this case, if the atmospheric temperature is low and the atmospheric-temperature vaporizing coil part 10 is frosted, the sampled LNG is preliminarily heated by using an auxiliary heating source in the preceding step, and thereafter vaporized by an atmospheric heat. Warm water, a warm wind, an electric heater or the like is used as the auxiliary heating source. The atmospheric-temperature vaporizing coil part 10 is wound spirally, and is an atmospheric-type heat exchanger in the wide sense, and includes a finned tube type. Needless to say, a heat transfer area enough to vaporize LNG completely, corresponding to the atmospheric temperature and the quantity of LNG to be vaporized is to be secured. ! (C)2000,JPO