The present invention addresses the problem of providing a skin collagen production-promoting agent that is free of safety problems. The present invention also addresses the problem of providing foods and drinks for promoting skin collagen production and cosmetic materials for promoting skin collagen production, which contain such a substance. Cystatins and/or cystatin decomposition products, obtained by decomposing cystatins with a protease such as pepsin or pancreatin, are used as the active ingredient of the skin collagen production-promoting agent, the foods and drinks for promoting skin collagen production, and the cosmetic materials for promoting skin collagen production. These cystatins and cystatin decomposition products have the effect of increasing the collagen content of skin.
