PURPOSE: To increase storage capacity and reliability by placing and engaging a group of external keys on an internal sphere equator member through an insulator on and in a group of internal keys spaced in circumferencial direction on an external sphere equator member to increase strength, supporting capacity and adiabatic property of the internal and external spheres.

CONSTITUTION: A whole double spherical tank with an internal and external spheres 1 and 2 is supported by means of skirts 3 connected to the outside of an external sphere equator member 6 by means of welding, etc. and the strength of the internal and external spheres 1 and 2 to vertical and horizontal loads can be maintained sufficiently by the external sphere equator member 6 and internal sphere equator member 5. Also, the internal sphere equator member 5 of the internal sphere 1 is placed and supported on the external equator member 6 through an insulator 7 and these members are engaged by means of a group of keys 8 and 9. The vertical load such as the weight of the internal sphere 1, extremely low temperature member a, etc. is transmitted to the skirts through the external sphere equator member 6 and invasion of heat is prevented due to presence of the insulator 7. The horizontal load acting on the internal sphere 1 is transmitted softly over a wide area of the internal and external sphere equator members 5 and 6 due to presence of the insulator 7 and to positioning of engagement by means of the group of keys 8 and 9.