A new peptide derivative is provided. The peptide derivative is represented by the following general formula (I),where polypeptide ExP is polypeptide that contains completely or partially the amino acid sequence of exendin-4, and a -L-Z group represents a group represented by the following formula (II) that is bonded to an amino acid side chain of or the α-amino group at the N-terminus of the polypeptide ExP,