An ester-based polymer to be used in the present invention has at least a repeating unit represented with the general formula (I). A and B are substituents substituted on a stilbene group. R1 is a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group. R2 is a linear or branched alkyl group having 2 to 10 carbon atoms. R3 to R6 each independently represents a hydrogen atom, a halogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group. n is an integer of 2 or more.