PURPOSE: To prevent the displacement of blocks while acquiring a drainage canal by forming a protruding or recessed section on the top face of the synthetic-resin foamed block and the recessed or projecting section to an underside thereof, respectively fitting and accepting the blocks when the blocks are laminated and making the depth of the recessed section smaller than the projecting section.

CONSTITUTION: The top face 2 or underside 3 of a synthetic-resin foamed block 1 has a plurality of projecting sections 4 while the underside 3 or the top face has recessed sections 5 accepting a plurality of the projecting sections 4. The depth of the recessed sections 5 is made smaller than the height of the projecting sections 4. When the blocks 1 are connected and laminated, slight clearances are formed among each block, and the clearances are used as drainage canals. Mutually acceptable irregularities are also shaped to the side faces of the blocks 1. Accordingly, the mutual displacement of the blocks 1 due to shocks and vibrations at the time when the blocks 1 are laminated can be prevented.