PURPOSE: To move a tank in a short period of time and inexpensively by providing a dike for enclosing an existing ground tank and a temporary installation space formed adjacent to the existing tank, filling the dike draining water in from so as to float and move the existing tank.

CONSTITUTION: A temporary installation space 4 is formed adjacent to an existing ground tank 1 constructed on the ground 2 to store LPG, LNG and the like, and a dike 6 for surrounding the existing ground tank 1 and the temporary installation space 4, is provided. After separating the ground tank 1 from the ground 2, water is filled in the dike 6 and the ground tank 1 is floated up and thereafter it is once transferred to the temporary installation space 4. Water in the dike 6 is then drained and a concrete made tank body 13 is built inside the dike 6. The dike 6 is filled with water again so as to float up the ground tank 1 and transfer it into the concrete made tank body 13. Water in the dike 6 is then drained and ground tank 1 is installed.