To provide a vertical water tank, in which an area in the horizontal plane direction may be reduced and the penetration of water on the outside and the leakage of water due to cracking, etc., can be prevented when the water tank is constructed in a ground, and a constructing method thereof.

Cylindrical bodies 15 made of steel are pressed into a ground by a method of press-in construction through a cutting edge 19 installed to a lower end port. Split rings 1 are joined in the peripheral direction and further connected in the axial direction in the cylindrical bodies 15 made of steel. Cylindrical bodies 51 made of precast concrete are mounted on the insides of the cylindrical bodies 15 made of steel after press-in. Not only the ground 39 of a bottom section is improved solidly by a method of high-pressure jet infection construction but also a waterproofing sheet 43 is laid, concrete is further placed on the sheet 43, and bottom concrete 41 is formed.