A foldable display device, comprising: a flexible display panel comprising a first display region, a second display region and a folding region between the first and second display regions that are configured to be relatively folded with respect to each other about the folding region; an upper case positioned at the peripheral area of the upper surface of the flexible display panel, the upper case including a frame structure having a first frame member, a second frame member, a third frame member and two flexible frame members, the first frame member and the second frame member disposed at opposite lateral sides of the flexible display panel and extending across the first display region, the second display region and the folding region, and the third frame member coupled to the rear surfaces of the first frame member and the second frame member and connecting one end of the first frame member to one end of the second frame member, wherein the flexible frame members are provided at the first frame member and the second frame member so as to be positioned at the folding region; a mid-frame coupled to the rear surface of the flexible display panel to support the flexible display panel, and extending across the first and second display regions (111, 112) and the folding region, wherein a plurality of holes are formed in a portion of the mid-frame that corresponds to the folding region; a second case coupled to the rear surface of the mid-frame to support the mid-frame and extending across the first display region; a hinge part coupled to the rear surface of the mid-frame at a location overlapping with the location of the plurality of holes in the mid-frame, the hinge part coupled to a lateral surface of the second case along a direction perpendicular to the direction of the lateral sides of the flexible display panel; and a third case provided on the rear surface of the second case and configured to support the second case, wherein the hinge part is configured to be folded when the upper surfaces of the first display region and the second display region are folded towards each other at an acute angle or an obtuse angle or a right angle; wherein the flexible display panel is configured to be folded along the edge of the hinge part, without folding the hinge part, so that the second display region is maintained on the rear surface of the third case. a flexible display panel comprising a first display region, a second display region and a folding region between the first and second display regions that are configured to be relatively folded with respect to each other about the folding region; an upper case positioned at the peripheral area of the upper surface of the flexible display panel, the upper case including a frame structure having a first frame member, a second frame member, a third frame member and two flexible frame members, the first frame member and the second frame member disposed at opposite lateral sides of the flexible display panel and extending across the first display region, the second display region and the folding region, and the third frame member coupled to the rear surfaces of the first frame member and the second frame member and connecting one end of the first frame member to one end of the second frame member, wherein the flexible frame members are provided at the first frame member and the second frame member so as to be positioned at the folding region; a mid-frame coupled to the rear surface of the flexible display panel to support the flexible display panel, and extending across the first and second display regions (111, 112) and the folding region, wherein a plurality of holes are formed in a portion of the mid-frame that corresponds to the folding region; a second case coupled to the rear surface of the mid-frame to support the mid-frame and extending across the first display region; a hinge part coupled to the rear surface of the mid-frame at a location overlapping with the location of the plurality of holes in the mid-frame, the hinge part coupled to a lateral surface of the second case along a direction perpendicular to the direction of the lateral sides of the flexible display panel; and a third case provided on the rear surface of the second case and configured to support the second case, wherein the hinge part is configured to be folded when the upper surfaces of the first display region and the second display region are folded towards each other at an acute angle or an obtuse angle or a right angle; wherein the flexible display panel is configured to be folded along the edge of the hinge part, without folding the hinge part, so that the second display region is maintained on the rear surface of the third case.