PURPOSE: To provide a wave breaking structure easy to mold by providing a thick plate formed with rows of openings of such a size as to prevent the escape of filler material such as concrete blocks and stone blocks and extendingly providing a support member for supporting the plate upright on the back face of the plate.

CONSTITUTION: A sideways-long oblong thick plate 1 made of reinforced concrete is provided in its upper and lower portions with a row of five vertically long oblong openings 2 extending from the front face to the back face, and provided with leg portions 1' at the ends of the long bottom side la. The size of the openings 2 is so selected as to prevent the escape of filler material such as stone blocks and concrete blocks. A wall block is composed of the thick plate 1 and a support member 4. The wall block is easily molded by mounting a pre-molded production mold for the thick plate 1 horizontally on a desired stand, assemblying a production mold for the support member 4 at the predetermined position of the former mold, and casting concrete in the molds.