PROBLEM TO BE SOLVED: To obtain a gentle slope bank block capable of expanding the growing area of sea algae growing in tidal zone by using a porous concrete body or its lower part having a specific constitution to control the water-retaining and water-discharging functions. SOLUTION: The porous concrete body or its lower part is made to have a laminated or box-shaped composite structure with a plain concrete and the aggregate particle size of the upper porous concrete is adjusted to control the water-retaining and water-discharging functions. A fit-in porous concrete plate may be used as the upper face. Plural parallel grooves may be formed at the center or at both sides of the upper face as wave-guiding grooves for guiding the wave to the high level.
