A flexible display device comprising: a support substrate having a first thickness and made of a first material, wherein the support substrate includes first and second faces which are opposite to each other; a buffer substrate disposed on the first face of the support substrate, wherein the buffer substrate has a second thickness smaller than the first thickness and is made of a second material more flexible than the first material; a thin-film transistor array disposed on the buffer substrate, wherein the buffer substrate is disposed between the thin-film transistor array and the support substrate; an organic light-emitting element array disposed on the thin-film transistor array; a sealing substrate fixedly disposed on the organic light-emitting element array, wherein the thin-film transistor array is disposed between the buffer substrate and the organic light-emitting element array; a polarization film disposed on the second face of the support substrate; and a rolling-assisting film disposed on the sealing substrate, wherein the sealing substrate is disposed between the rolling-assistant film and thin-film transistor array, wherein the rolling-assistant film comprises a base and a pattern of a plurality of ribs disposed in the base and spaced apart by a predetermined distance, wherein the ribs are arranged in a direction corresponding to a rolling direction of the flexible display device, wherein the first material includes glass, and wherein the second material includes one selected from a group consisting of polyethylene terephthalate, PET, ethylene naphthalate, PEN, polyimide, PI, polymethyl methacrylate, PMMA, polycarbonate, PC, polystyrene, PS, and polyethersulfone, PES. a support substrate having a first thickness and made of a first material, wherein the support substrate includes first and second faces which are opposite to each other; a buffer substrate disposed on the first face of the support substrate, wherein the buffer substrate has a second thickness smaller than the first thickness and is made of a second material more flexible than the first material; a thin-film transistor array disposed on the buffer substrate, wherein the buffer substrate is disposed between the thin-film transistor array and the support substrate; an organic light-emitting element array disposed on the thin-film transistor array; a sealing substrate fixedly disposed on the organic light-emitting element array, wherein the thin-film transistor array is disposed between the buffer substrate and the organic light-emitting element array; a polarization film disposed on the second face of the support substrate; and a rolling-assisting film disposed on the sealing substrate, wherein the sealing substrate is disposed between the rolling-assistant film and thin-film transistor array, wherein the rolling-assistant film comprises a base and a pattern of a plurality of ribs disposed in the base and spaced apart by a predetermined distance, wherein the ribs are arranged in a direction corresponding to a rolling direction of the flexible display device, wherein the first material includes glass, and wherein the second material includes one selected from a group consisting of polyethylene terephthalate, PET, ethylene naphthalate, PEN, polyimide, PI, polymethyl methacrylate, PMMA, polycarbonate, PC, polystyrene, PS, and polyethersulfone, PES.