PURPOSE: To improve the heat insulating performance of a space part between an inner and an outer tanks compared to the case of non-vacuum heat insulating structure.

CONSTITUTION: An outer tank 4 is disposed outside of an inner tank 3 formed to store low temperature liquid 2. Vacuum balls 7 made of material with low heat conductivity are filled in a space part 5 between the inner and outer tanks 3, 4, and heat insulating material powder is filled in gaps among the respective vacuum balls 7. A vacuum area by the vacuum balls 7 is formed in the non- vacuum heat insulating structure by heat insulating material powder so as to put the space part 5 in a state close to a vacuum, thus heightening heat insulating performance.