PURPOSE: To eliminate the needs for repairing work for long periods of time by tensely providing plural protective plates on the surface of the sloped ground in an artificial islet having a sloped surface on its surrounding.

CONSTITUTION: On the surface of a sloped surface K provided for relaxing icing force on the surrounding of an artificial islet E, slope protective plates 10 consisting of protective plates 11 made of a slippery and strong surface-treated material, e.g., iron, steel, stainless steel, etc., having fixing materials 12 projectionally provided in a latticed form at a given interval on their downsides, are tensely provided. The artificial islet E can thus be exactly protected from the forces of ice growing and coming and also of wind and tidal waves.