A precursor of molecular probe for imaging of pancreatic islets is provided. A polypeptide represented by any one of the following formulae (1) to (4), or a polypeptide having a homology with the foregoing polypeptide. *-DLSK* QMEEEAVRLFIEWLK* NGGPSSGAPPPSK-NH 2 (1) *-LSK* QMEEEAVRLFIEWLK* NGGPSSGAPPPSK-NH 2 (2) *-SK* QMEEEAVRLFIEWLK* NGGPSSGAPPPSK-NH 2 (3) *-K* QMEEEAVRLFIEWLK* NGGPSSGAPPPSK-NH 2 (4), in the foregoing formulae (1) to (4) *- indicates that an ±-amino group at an N-terminus is protected by a protecting group or modified with a modifying group having no electric charge K* indicates that an amino group of a side chain of a lysine is protected by a protecting group and -NH 2 indicates that a carboxyl group at a C-terminus is amidated.
