Abstract: A gravity structure such as caisson, concrete block or L-shaped block that is used in the construction work of breakwaters, seawalls, and wharfs. The gravity structure of the invention is stable and hardly moved by external force such as wave force, and is characterized in that a plurality of unit friction members are disposed in the bottom surface of a concrete body, said unit fraction members increasing the coefficient of friction between the surface of foundation and said concrete body, and said unit friction members are so embedded integrally in said concrete body that the bottom surfaces of unit fraction members are brought into contact with the foundation surface.