PURPOSE: To easily and surely connect floating units together on the ocean by arranging chamber parts, which are connected with adjacent floating units so as to form a watertight working barrier, in the outer circumference positions of respective floating units and arranging a connecting means in the working barrier position for connecting them together.

CONSTITUTION: In a floating unit 1, whose horizontal shape is a square, an upper floor plate 2 and a lower floor plate 3 are divided by vertical barriers 4 into a grid, so that plural barriers 5 are formed in the inside the grid. A chamber part, 6 opened to a connecting face side is arranged in the outer circumference position equivalent to each side of the square, and a watertight working barrier 7 is formed by connecting the adjacent floating units 1 on the ocean. PC steel products 8 for this connection are arranged from the outside and the inside of the working barrier 7 while they are in dry conditions, and after installation of the PC steel products 8, concrete is put in the inside of the working barrier 7, and consequently, the floating units 1 are integrated with each other. Then, prestress is applied in the connection parts by stressing the PC steel products 8.