To prevent moment deformation at the thin-walled portion around a support for a tank shell by providing the support with a tank shell supporting point on the shaft in the thickness direction of the tank shell, the support being formed with a spherical joint between a supporting shaft mounted on a fixture and the tank shell.

Relatively thin bosses 1b are provided at several (three or four) positions on a thin-walled spherical tank shell 1a to support a tank. The bosses 1b are fixed with a holddown for which a recessed spherical face 2b combined with a protruded spherical face 2a provided at the end of a supporting shaft 2 to form a spherical joint is mounted on the bosses 1b with bolts 12. A support for time tank shell 1a is formed with the spherical joint. In the boss 3a at the end of a bracket 3 fixed to a base plate 11 via an heat insulating material 8 and a heat insulating spacer 7 with a bolt 6, the supporting shaft 2 and a shaft opposed to the protruded spherical face 2a are inserted to support the supporting shaft 2.