Use of a molecular probe for imaging of pancreatic islets, the molecular probe comprising any one of the following polypeptides: a polypeptide represented by any one of the following formulae to and to; or a polypeptide having a homology of 95% or higher with any one of the amino acid sequences of polypeptides represented by the following formulae to, the polypeptide comprising the α-amino group at the N-terminus labeled with a group represented by the formula below, and no other labeling group, and the amidated carboxyl group at the C-terminus and being capable of binding to pancreatic islets, Z-DLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 1) Z-LSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 2) Z-SXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 3) Z-XQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 4) B-DLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 9) B-LSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 10) B-SKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 11) B-KQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 12) where in the foregoing formulae to, Z- indicates that the α-amino group at the N-terminus is either not modified, or is modified with a modifying group having no electric charge, and X represents a lysine residue, the amino group of the side chain of the lysine residue being labeled with a group represented by formula below, in the formulae to, B- indicates that the α-amino group at the N-terminus is labeled with a group represented by formula below, and in the foregoing formulae to and to, -NH 2 indicates that the carboxyl group at the C-terminus is amidated, where R 1 represents a substituent that contains any one of 123 I, 124 I, 125 I, and 131 I. a polypeptide represented by any one of the following formulae to and to; or a polypeptide having a homology of 95% or higher with any one of the amino acid sequences of polypeptides represented by the following formulae to, the polypeptide comprising the α-amino group at the N-terminus labeled with a group represented by the formula below, and no other labeling group, and the amidated carboxyl group at the C-terminus and being capable of binding to pancreatic islets, Z-DLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 1) Z-LSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 2) Z-SXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 3) Z-XQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 4) B-DLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 9) B-LSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 10) B-SKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 11) B-KQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 12) where in the foregoing formulae to, Z- indicates that the α-amino group at the N-terminus is either not modified, or is modified with a modifying group having no electric charge, and X represents a lysine residue, the amino group of the side chain of the lysine residue being labeled with a group represented by formula below, in the formulae to, B- indicates that the α-amino group at the N-terminus is labeled with a group represented by formula below, and in the foregoing formulae to and to, -NH 2 indicates that the carboxyl group at the C-terminus is amidated, where R 1 represents a substituent that contains any one of 123 I, 124 I, 125 I, and 131 I. Z-DLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 1) Z-LSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 2) Z-SXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 3) Z-XQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 4) B-DLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 9) B-LSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 10) B-SKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 11) B-KQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO. 12)