A flexible display device is disclosed. The flexible display device includes a first body, a second body, a flexible display, a first rack, a second rack, a first gear, and a second gear. The first gear and the second gear rotate in conjunction with each other. The flexible display is divided into a first region and a second region, and the second rack forms a continuous loop together with the second region of the flexible display. Accordingly, when the second body slides with respect to the first body, tension can be stably applied to the flexible display, and the flexible display is prevented from being loosened.