PURPOSE: To obtain an artificial beach having natural purifying capability by forming a water-permeable wave dissipation bank and foundation consolidating masonry sunken- rocks at the earth tip of a breakwater, and by arranging a submerged breakwater, a water-permeable sand stopper, and a sandy beach between the breakwater and the water dissipation bank.

CONSTITUTION: On the respective surfaces of a water-permeable wave dissipation bank 2, a water-passing course in the bank 2 and a foundation consolidating masonry sunken-rocks 3, a submerged breakwater 4, and a water-permeable sand stopper 5 in the offing of a breakwater 1, the organic corrupted substance of the cause of the pollution of seawater due to the attachable filtered edible living things of attachably living hard-shelled mussels, barnacles, and the like is converted to the organic fine pieces of the food of lugworms, crabs, and the like, and is reduced. Then, nitrogen or the like to be the nourishing source of planktons is absorbed into seaweeds growing thick to make nourishing salts inorganic with nitrification bacteria or the like living on the bank 2, the sunken rocks 3, the submerged breakwater 4, the sand stopper 5, and sand 6. After that, organic substance piled up on the surface of the sea bottom is made inorganic with trepangs and is turned into sea bottom soil. As a result, biological clarification can be performed.