PROBLEM TO BE SOLVED: To provide an external preparation for skin, suitable for preventing wrinkle formation and rough skin by promoting collagen production, specifically by promoting collagen production in human skin fibroblasts.SOLUTION: The inventors have found that a conchiolin hydrolysate is effective to promote collagen production and have expanded its use. They also have found that, when used as an origin of conchiolin, black-lip pearl oysters are effective to promote collagen production.