PURPOSE: To simply install an underwater structure on a foundation in a short time by a method in which a flexible tire whose lower part is fixed to the foundation and the upper end is provided with a screw portion is fitted into and fixed to the notched portion of the peripheral edge of the underwater structure.

CONSTITUTION: The lower part of a flexible tire 3 with an upper end 4 is buried in the foundation 1 and fixed to an anchor frame 2, and a notched portion 6 is formed on the peripheral edge 5A of an underwater structure 5. The foundation 1 is first set on the seabed, the underwater structure 5 is settled and installed in place on the foundation 1, and the upper part of th flexible tire 3 in a state as shown by an imaginary line is turned and fitted into the notched portion 6 of the foundation 1. Then, a washer 7 is screwed with the screw portion 4 with the nut 8. As needed, the lower part of the underwater structure 5 is hardened with concrete 9.