PURPOSE: To construct a water tank with an excellent stability in the strength, and having a high processing freedom which permits to construct by utilizing the plot effectively.

CONSTITUTION: A water tank 1 is composed of the aggregate of angular tube form divided chambers 3 constructed on a base concrete 2. Corner columns 5 erected at the corners of the constructing water tank 1; the first intermediate columns 6 erected at the necessary positions between neighboring corner columns 5; and the second intermediate columns 7 erected at the necessary positions of spaces surrounded by the corner columns 5; are provided. The various columns are erected by positioning at the crossing points of latticeworks. Furthermore, wall plates 9 are used to cover between the coupling surfaces of opposing columns, and the upper ends of the divided chambers 3 are blocked by lid plates 10.