A flexible display device includes: a display panel including a display substrate, an organic light emitting element formed on the display substrate, and a thin film encapsulation layer covering the organic light emitting element; a first insulation layer formed under the display panel; a lower protection film formed under the first insulation layer; and a reinforcement layer formed under the lower protection film, between the lower protection film and the first insulation layer, or on the display panel, wherein the reinforcement layer is configured to prevent damage to the display panel due to bending stress.