A foldable display device includes a display panel which includes a folding area and non-folding areas on some sides of the folding area, and a hinge unit which is disposed in an area corresponding to the folding area below the display panel to in-fold or out-fold the display panel. The hinge unit includes a plurality of rotary shafts and a plurality of coupling links disposed between the plurality of rotary shafts. Accordingly, the foldable display device can be bi-directionally (e.g., inwardly or outwardly) folded by the hinge unit with a simple structure. Further, a radius of curvature during the folding can be desirably changed by adjusting a component of the hinge unit, for example, a number of the plurality of rotary shafts and the plurality of coupling links, a cross-sectional length, and the like.