To prevent a tube from generating its freezing phenomenon, by cooling the air, which is supplied as a gasifying heat source, to a temperature of 0°C or less thereafter allowing this air to flow performing forced convection in an external surface of the air warming tube. CONSTITUTION: Liquefied natural gas (LNG) is fed to an air warming tube 3 from an LNG feed-in line 1. While the air for gasification is fed into a blown air passage 12 from a fan 5 being cooled to 0°C in a heat exchanger 6 thereafter reaching the air warming tube 3, and the air, which heats the LNG to be gasified, is discharged from an exhaust port 12a. Gasifying the LNG in the air warming tube 3, the LNG, after its superheating is performed in a superheater 4, is fed out to a consumption side via a feed-out line 2. Here water in the air, cooled to o°C, changes into snow pieces or freezes, but the snow piece or frozen water, which collides against a baffle plate 10 dropping down to the bottom part of the blown air passage 12, changes into water being removed from a drain valve 11.