Provided is a horny layer function improving agent containing at least one D-amino acid selected from the group consisting of D-arginine, D-histidine, D-leucine, D-tyrosine, D-valine, D-allo-threonine, D-lysine, D-tryptophan, D-allo-isoleucine, D-asparagine, D-phenylalanine, and D-glutamine as an active ingredient.