A molecular probe precursor for islet imaging is provided. A polypeptide represented by any one of the following formulas (1) to (12) or a polypeptide having homology with the polypeptide. * -DLSKQMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 (1) *-LSKQMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 (2) *-SKQMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 (3) *-KQMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 (4) * SG4PS-PS2 * 4 * -LSK * QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (6) *-SK * QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (7) *-K * QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (8) DLSK * QMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 * 9EELSRLQPSLKME * EE SK * QMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 (11) K * QMEEEAVRLFIEWLK * NGGPSSGAPPPS-NH2 (12)膵島イメージング用分子プローブ前駆体を提供する。下記式(1)~(12)のいずれかで表されるポリペプチド又は前記ポリペプチドと相同性を有するポリペプチド。*-DLSKQMEEEAVRLFIEWLK*NGGPSSGAPPPS-NH2(1)*-LSKQMEEEAVRLFIEWLK*NGGPSSGAPPPS-NH2(2)*-SKQMEEEAVRLFIEWLK*NGGPSSGAPPPS-NH2(3)*-KQMEEEAVRLFIEWLK*NGGPSSGAPPPS-NH2(4)*-DLSK*QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2(5)*-LSK*QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2(6)*-SK*QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2(7)*-K*QMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2(8)DLSK* QMEEEAVRLFIEWLK* NGGPSSGAPPPS-NH2(9)LSK* QMEEEAVRLFIEWLK* NGGPSSGAPPPS-NH2(10)SK* QMEEEAVRLFIEWLK* NGGPSSGAPPPS-NH2(11)K* QMEEEAVRLFIEWLK* NGGPSSGAPPPS-NH2(12)