a of the main unit 11 in such a manner that the discharge port 18 communicates with the seawater inlet passage 13 so that the bubbling air 15 is swiftly discharged according to the present embodiment the heat exchanging tube 14 is for example a trombone shaped spiral tube so that heat exchange efficiency is enhanced however the present invention is not to be thus limited and a tube of any shape having high heat exchange efficiency may be applied according to the present embodiment the heat exchanging tube 14 includes a flange joint 19 and is separable into multiple parts thus the heat exchanging tube 14 can be separated or connected when the heat exchanging tube 14 is to be inserted into or removed from the seawater inlet passage 13 thereby making insertion or removal of the heat exchanging tube easier according to the present embodiment the seawater inlet port 13 a is located below the discharge port 18 thereby increasing efficiency in supplying seawater and increasing the heat exchange efficiency according to the present embodiment the air supplying device 17 supplies air to the bubbling device 16 and an airlift force of the bubbling causes the seawater 12 to be brought inside the seawater inlet passage 13 then lng is supplied into the heat exchanging tube 14 thus heat exchange is caused between the lng and the seawater 12 to vaporize the lng into ng according to the present embodiment providing the lng gasifier for example to a ship to be an fpso it is possible to realize a stable vaporization of lng thus an lng gasifier that has a simple structure in which a seawater pump for supplying a heat source which is required in a conventional lng gasifier.