Providing a peptide derivative represented by the following general formula (I). In the formula (I), polypeptide ExP indicates a polypeptide having partially or completely the amino acid sequence of exendin-4, or the side chain of the amino acids of the polypeptide of the N-terminal ExP -L-Z group, α - is a group represented by the following formula to bind to the amino group (II).下記一般式(I)で表されるペプチド誘導体の提供。式(I)において、ポリペプチドExPは、exendin-4のアミノ酸配列を完全に又は部分的に有するポリペプチドを示し、-L-Z基は、ポリペプチドExPのアミノ酸の側鎖又はN末端のα-アミノ基に結合する下記式(II)で表される基である。