The present invention provides a novel active ingredient which can be safely used in preventing, ameliorating or treating diseases related to the cartilage such as cartilage damages and cartilage disorders. Since the egg yolk protein hydrolyzate has an effect on chondrocyte proliferation promotion, it is useful as an active ingredient for preventing, ameliorating or treating cartilage disorders and for preventing, ameliorating or treating joint pain. The egg yolk protein hydrolyzate is a natural-origin material with high safety and, therefore, can be widely used in foods and drinks, medicines, feeds and the like which can be daily ingested.