PURPOSE: To save the amount of tank structure material and reduce the weight of tank main body by improving the plate thickness distribution of a spherical shell comprising a tank.

CONSTITUTION: In a roughly spherical liquified gas tank 1 to be mounted on a liquified gas carrying vessel 3, a plate thickness of the a spherical shell 4 forming the tank is provided with a nonaxisymmetric distribution around its vertical axis, and a spherical shell sections in bow and stern directions are provided with a thinner plate thickness than the spherical sections in port and starboard directions for band spherical sections at the same height.