A flexible display device including a flexible display panel which displays an image, a strain gauge disposed in the flexible display panel, where the strain gauge senses a strain in the flexible display panel and generates a detection signal based on the sensed strain, a strain controller which receives the detection signal and outputs a strain compensation voltage based on the detection signal, and a strain compensation layer disposed on a surface of the flexible display panel and which receives the strain compensation voltage, where a thickness of the strain compensation layer may be controlled based on the strain compensation voltage such that a neutral plane of the flexible display device is maintained in a predetermined reference area in the flexible display panel.