A foldable display device includes a flexible display module and a first plate. The flexible display module includes a foldable area and the non-foldable area. The foldable area includes a first area, a second area spaced apart from the first area and disposed in at least two sides of the first area, and a third area disposed between the first area and the second area. The non-foldable area is disposed in at least two sides of the foldable area. The first plate is disposed under the flexible display module. The first plate includes a plurality of grooves overlapping the second area and penetrating the first plate. The first plate overlapping the third area does not include grooves.