PROBLEM TO BE SOLVED: To provide a transglutaminase activator that activates transglutaminase, a ceramide production accelerator that accelerates production of ceramide, and an involucrin expression accelerator that accelerates expression of involucrin.SOLUTION: A transglutaminase activator, a ceramide production accelerator, and an involucrin expression accelerator comprise an extract of a plant Peristrophe japonica as an active ingredient.