PURPOSE: To provide a gravity type structure like caisson and concrete block used for constructing breakwater or bank for protecting reclaimed land, which is protected against sliding when an external force is acted thereto, by providing plurality of unit frictional members under the lower surface of a concrete block.

CONSTITUTION: A plurality of unit frictional members 2 made of rubber are fixedly placed under the lower surface of concrete block 1a. These unit frictional members 2 are embedded in the body of concrete block 1a by use of fixing metal means 3 and reinforcing steel bars 4. The fixing metal means 3 consists of retainer plate portion 3a and ribs 3b, and the plate portion 3a is embedded in rubber blocks 2 so that rubber blocks 2 and means 3 are coupled together in a unitary manner. On the other hand, ribs 3b are projected above the back surface of rubber blocks 2 and reinforcing bars 4 arranged in concrete block 1a are extended through the ribs 3b. The ribs 3b are arranged in the form of a cross and fixed firmly to longitudinal and lateral bars 4. By thus embedding a plurality of frictional members 2 in the lower surface of concrete block 1a, it is enabled to increase the frictional factor and hence to obtain a highly stable gravity type structure.