A liquid hydrogen vaporizer for performing heat exchange between liquid hydrogen and helium gas and vaporizing liquid hydrogen, comprising: a lower first column tube which is a fin tube composed of a tube through which liquid hydrogen flows and a fin assembly attached to an outer periphery of the tube; and a lower casing through which helium gas flows outside the lower first column tube, wherein the fin assembly is composed of a sleeve covered on an outer surface of the tube and a plurality of fins attached to an outer peripheral surface of the sleeve, and the sleeve is slidable in a longitudinal direction of the tube.