PURPOSE: To eliminate a bad influence caused by the range of tide in a specific half-submerged structure each as a restaurant and underwater observation device used for leisure time amusement and sports.

CONSTITUTION: A base 7 is installed on the underwater ground, and a column 2 is erected from the base 7 to support a structure body 1a. In a half-submerged structure comprising a part of the structure body 1a submerged in water, the column 2 is made vertically elastic. In addition, a damper 3 is provided on the column 2 to damp the impact caused by the vertical motion of the structure body 1a, and the, floating half-submerged structure 1 is formed in such a way that the structure body 1a may keep its height at a specified value to the water surface 5a.