To recycle wastes by placing ordinary concrete or coal ash concrete around the cubical mass of waste plastics melted and solidified.

Concrete or coal ash concrete 2 is placed around a rectangular parallelepiped cubical mass 1 of waste plastics melted and solidified thereby forming a cubical mass block 3. Next, after placing concrete 2 in the bottom portion of a formwork 4, dowels 5 are arranged on the side surface, the cubical mass 1 is installed at the central part of the formwork 4, concrete 2 is placed on the top of the side surface thereby forming the cubical mass block 3. Or after installing a plurality of cubical masses 1 at proper intervals on concrete at the bottom of formwork 4, concrete is placed almost in the same manner, the cubical mass 1 is stacked on the top portion of concrete and, in the same manner, concrete is poured. Then, a number of the blocks 3 are placed in the sea in multiple stages for example, and a breeding, rising, start flow type mound-shaped gathering place for fish is provided on the sea floor, thereby recycling a large amount of wastes which can be used easily for production and installation work.