A primary object of the present invention is to develop a compound that specifically inhibits the production of A² protein and serves as an active ingredient of a drug to treat and/or prevent Alzheimer's disease. This object can be achieved by a polypeptide having the amino acid sequence represented by any one of SEQ ID NOs: 1, 13, 14, and 22, that binds to the N-terminal region of ²CTF； a ³-secretase activity inhibitor containing the polypeptide； ²-secretase activity inhibitor； A² protein production inhibitor； and an agent for treating and/or preventing Alzheimer's disease.
