Foldable display device

A foldable display device includes a display panel including a folding area and a non-folding area, and a support substrate disposed under the display panel, the support substrate includes a first metal sheet including a plurality of wavy curved portions and a first planarization layer disposed on the first metal sheet, and the support substrate includes a second metal sheet disposed on the first planarization layer and having a planar surface shape and a second planarization layer disposed under the first metal sheet, therefore, since the support substrate integrated into a single layer is disposed under the display panel, folding properties of the display device may be improved, and an overall thickness of the display device may be decreased and a transfer of a pattern boundary or a folding area boundary can be minimized.