A molecular probe for use in imaging of pancreatic islets is provided. The molecular probe comprises a polypeptide represented by the following formula (1), (2), or (3), or a polypeptide having homology with the foregoing polypeptide, (SEQ ID NO. 1) Z-HGEGTFTSDLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (1) (SEQ ID NO. 2) Z-HGEGTFTSDLSKQMEEEAVRLFIEWLXNGGPSSGAPPPS-NH2 (2) (SEQ ID NO. 3) B-HGEGTFTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (3) where, in the formulae (1) and (2), “X” represents a lysine residue, an amino group of a side chain of the lysine residue being labeled with a radioactive nuclide, and “Z—” indicates that an α-amino group at an N-terminus is not modified, or is modified with a modifying group having no electric charge; in the formula (3), “B—” indicates that an α-amino group at an N-terminus is labeled with a radioactive nuclide; and in the formulae (1), (2), and (3), “—NH2” indicates that a carboxyl group at a C-terminus is amidated.