A cell-penetrating peptide described in any of (A) to (D) below gives cell membrane permeability and further transmucosal absorbability to a physiologically active substance:(A) a peptide having the amino acid sequence represented by SEQ ID NO:1；(B) a peptide having an amino acid sequence which is the same as the amino acid sequence represented by SEQ ID NO:1 except that one or several basic amino acids are substituted, deleted, inserted and/or added, which peptide has cell membrane permeability；(C) a peptide having an amino acid sequence which is the same as the amino acid sequence represented by SEQ ID NO:1 except that 1 to 5 amino acids are substituted, deleted, inserted and/or added, which peptide has cell membrane permeability；(D) a peptide having: an amino acid sequence represented by the reverse sequence of any of (A) to (C)； an amino acid sequence which is the same as the amino acid sequence represented by the reverse sequence of (A) except that one or several basic amino acids are substituted, deleted, inserted and/or added； or an amino acid sequence which is the same as the amino acid sequence represented by the reverse sequence of (A) except that 1 to 5 amino acids are substituted, deleted, inserted and/or added； which peptide has cell membrane permeability.
