A polymeric fluorescent substance having visible fluorescence in a solid state and a polystyrene-reduced number-average molecular weight of 103 to 107, which contains at least one repeating unit represented by the following formula (1), —Ar1—CR1═CR2—  (1) wherein the sum of the repeating unit is from 10 to 100 mol % of the total number of the repeating units, Ar1 represents an arylene group having 4 to 20 carbon atoms taking part in conjugated bonds and containing at least one substituent represented by the following formula (2) as a nuclear substituent, or a heterocyclic compound group, having 4 to 20 carbon atoms taking part in conjugated bonds, and containing at least one substituent represented by the following formula (2) as a nuclear substituent; and R1 and R2 independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms and a cyano group, —(X)m—(CH2)n—Ar2  (2) wherein Ar2 represents a group selected from the group consisting of an aryl group and having 4 to 20 carbon atoms taking part in conjugated bonds, a heterocyclic compound group, having 4 to 20 carbon atoms taking part in the conjugated bonds, and an aliphatic cyclic hydrocarbon compound group having 6 to 20 carbon atoms constituting the ring; X represents O or S; m represents 0 or 1; and n represents an integer of 2 to 10. The polymeric fluorescent substance is excellent as a material for organic EL devices because of strong fluorescence and good thermal stability. Furthermore, an organic EL device using the polymeric fluorescent substance can be preferably used as a flat light source for back light or a device such as a flat panel display and the like because it is easily produced and exhibits excellent light emitting characteristics and a heat resistance.