A saccharide-measuring fluorescence sensor substance including a copolymer of at least the following two compounds (I) and (II) is provided: (I) a fluorescent monomer compound represented by the following formula (1): formula (1) wherein: Q, Q′ and D3 may be the same or different, may be combined together into a fused ring, and are each a substituent selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, and substituted or unsubstituted alkyl, acyl, oxyalkyl, carboxyl, carboxylate ester, carboxamido, cyano, nitro, amino and aminoalkyl groups; and D1, D2 and D4 each represent a substituent, wherein at least one of D1, D2 and D4 is a substituent group comprising a vinyl group at an end thereof, and wherein the substituent group comprising a vinyl group at an end thereof enables the fluorescent monomer compound to be soluble in water, and (II) at least one hydrophilic, polymerizable monomer having a vinyl group.