To provide an artificial island having a half-floating structure and a method for the execution thereof which does not produce unequal ground subsidence, but can easily build a partition wall on the sea in a short work period and economical work cost without needing of embedding a great amount of earth.

An iron box ship 1 as a hollow floating body is vertically movably held near the upper end of a support post 3 having the lower end fixedly embedded in a rock floor, while a hollow fixing post 1 extending vertically through an iron box ship 1 and having the lower end embedded in the bottom of the sea is provided. Further, the interior of the fixing post 10 is filled with a reinforcing material like cement so that the iron box ship 1 is fixed in a predetermined position by the fixing post 10.