PROBLEM TO BE SOLVED: To provide an object that is usable daily, highly safe, and useful for dysarthrosis including denaturation of articular cartilage, or a composition containing the object.SOLUTION: An external preparation for skin contains a raw material containing seaweed calcium or calcium compound derived from the raw material containing seaweed calcium. Further, a composition for protecting cartilage and a composition for protecting joint contain a raw material containing seaweed calcium or a calcium compound derived from the raw material containing seaweed calcium.SELECTED DRAWING: Figure 1