PURPOSE: To incorporate a function to control the heating value of NG, based on a simple, compact structure and addition of LPG, into the function of the device.

CONSTITUTION: In an open rack type LNG vaporizer in which LNG inlet headers 10 and NG outlet headers 16 are connected by a plurality of LNG-vaporizing heating tubes 22 each of the outlet headers 16 is extended. To these extensions the upper ends of a plurality of LPG-vaporizing heating tubes 22' are connected and to NG-recovering inlet headers 10' the lower ends of the LPG-vaporizing heating tubes 22' are connected.