Use of a molecular probe for imaging of pancreatic islets, the molecular probe consisting of any one of the following polypeptides: a polypeptide represented by the following formula,, or; a polypeptide that is obtained by deletion, insertion, or substitution of one, two or three amino acids with respect to the polypeptide represented by the following formula,, or and that is capable of binding to pancreatic islets; a polypeptide that has a homology of 95% or higher with the amino acid sequence of the polypeptide represented by the following formula,, or and that is capable of binding to pancreatic islets; and a polypeptide that is obtained by deletion of 1 to 9 amino acids from the C-terminal end of the polypeptide represented by the following formula,, or and that is capable of binding to pancreatic islets or a polypeptide that has a homology of 95% or higher to the polypeptide obtained by said deletion and that is capable of binding to pancreatic islets: Z-HGEGTFTSDLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO.1) Z-HGEGTFTSDLSKQMEEEAVRLFIEWLXNGGPSSGAPPPS-NH 2 (SEQ ID NO. 2) B-HGEGTPTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NB 2 (SEQ ID NO. 3) where in formulae and, "X" represents a lysine residue, the amino group of the side chain of the lysine residue being labeled with a radioactive nuclide, and "Z-" indicates that the α-amino group at the N-terminus is not modified, or is modified with a modifying group having no electric charge, in formula, "B-" indicates that the α-amino group at the N-terminus is labeled with a radioactive nuclide, and in formulae,, and, "-NH 2 " indicates that the carboxyl group at the C-terminus is amidated, wherein homology is the value obtained by dividing the number of identical amino acids existing in two polypeptides to be compared, by the number of amino acids of the entire length of one of the polypeptides. a polypeptide represented by the following formula,, or; a polypeptide that is obtained by deletion, insertion, or substitution of one, two or three amino acids with respect to the polypeptide represented by the following formula,, or and that is capable of binding to pancreatic islets; a polypeptide that has a homology of 95% or higher with the amino acid sequence of the polypeptide represented by the following formula,, or and that is capable of binding to pancreatic islets; and a polypeptide that is obtained by deletion of 1 to 9 amino acids from the C-terminal end of the polypeptide represented by the following formula,, or and that is capable of binding to pancreatic islets or a polypeptide that has a homology of 95% or higher to the polypeptide obtained by said deletion and that is capable of binding to pancreatic islets: Z-HGEGTFTSDLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO.1) Z-HGEGTFTSDLSKQMEEEAVRLFIEWLXNGGPSSGAPPPS-NH 2 (SEQ ID NO. 2) B-HGEGTPTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NB 2 (SEQ ID NO. 3) where in formulae and, "X" represents a lysine residue, the amino group of the side chain of the lysine residue being labeled with a radioactive nuclide, and "Z-" indicates that the α-amino group at the N-terminus is not modified, or is modified with a modifying group having no electric charge, in formula, "B-" indicates that the α-amino group at the N-terminus is labeled with a radioactive nuclide, and in formulae,, and, "-NH 2 " indicates that the carboxyl group at the C-terminus is amidated, Z-HGEGTFTSDLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH 2 (SEQ ID NO.1) Z-HGEGTFTSDLSKQMEEEAVRLFIEWLXNGGPSSGAPPPS-NH 2 (SEQ ID NO. 2) B-HGEGTPTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NB 2 (SEQ ID NO. 3)