A cyclic peptide or a salt thereof of formula (1): X-Leu-Val-Y1-Y2 (1), where X is Lys, Arg, His, Ala, Gly, Ser, or Thr； and Y1 and Y2, which are identical to or different from each other, each represent a group represented by formula (2):where Ar1 represents an aromatic hydrocarbon group or an aromatic heterocyclic group； R1 represents a hydrogen atom, an alkyl group, a cycloalkyl group, a haloalkyl group, an aromatic hydrocarbon group, or an aromatic heterocyclic group； and n is an integer from 0 to 2. In the cyclic peptide has an α-amino group at the amino terminus of the amino acid sequence which is linked, via a peptide bond, to the carboxyl group at the carboxyl terminus of the amino acid sequence.
