Provided is a novel compound which has excellent inhibitory activity for A² aggregation, and which is useful as a drug. A cyclic peptide or a salt thereof, the cyclic peptide having an amino acid sequence represented by the following formula (1): €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒX-Leu-Val-Y 1 -Y 2 €ƒ€ƒ€ƒ€ƒ€ƒ(1) (wherein X is Lys, Arg, His, Ala, Gly, Ser, or Thr； and Y 1 and Y 2 , which are identical to or different from each other, each represent a group represented by the following formula (2) : (wherein Ar 1 represents an aromatic hydrocarbon group or an aromatic heterocyclic group (the aromatic hydrocarbon group or the aromatic heterocyclic group may have 1 to 5 substituents selected from the group consisting of an alkyl group, a cycloalkyl group, a haloalkyl group, a halogen atom, a hydroxy group, an alkoxy group, an aromatic hydrocarbon group, an aromatic heterocyclic group, and an amino group)； R 1 represents a hydrogen atom, an alkyl group, a cycloalkyl group, a haloalkyl group, an aromatic hydrocarbon group, or an aromatic heterocyclic group (the aromatic hydrocarbon group or the aromatic heterocyclic group may have 1 to 5 substituents selected from the group consisting of an alkyl group, a cycloalkyl group, a haloalkyl group, a halogen atom, a hydroxy group, an alkoxy group, an aromatic hydrocarbon group, an aromatic heterocyclic group, and an amino group)； and n is an integer from 0 to 2)), wherein the ±-amino group at the amino terminus of the amino acid sequence is linked, via a peptide bond, to the carboxyl group at the carboxyl terminus of the amino acid sequence.
