A foldable display device comprising: a support structure including a hinge, a plurality of supports (SP1, SP2) disposed on opposite sides of the hinge and physically coupled to the hinge, wherein a light transmitting area is defined in a portion of the supports (SP1, SP2); a foldable display panel disposed on a first surface of the support structure, and including a foldable display area corresponding to the hinge, and a plurality of display areas (DA1, DA2) disposed on opposite sides of the foldable display area; and an input sensor disposed in the light transmitting area of the support structure at a position spaced apart from the foldable display panel, wherein the light transmitting area corresponds to an opening defined in the support structure, characterized in that: a transparent insulating layer is disposed in the opening of the support structure, the input sensor is disposed on the transparent insulating layer, the transparent insulating layer is disposed between the input sensor and the foldable display panel when the foldable display panel is folded, and at least a portion of a sidewall of the opening of the support structure includes an inclined surface which is inclined with respect to a first direction perpendicular to the first surface of the support structure or to a second surface of the support structure facing the first surface, wherein a first width of the opening that is defined on a plane in an extension of the first surface of the support structure is greater than a second width of the opening that is defined on a plane in an extension of the second surface of the support structure. a support structure including a hinge, a plurality of supports (SP1, SP2) disposed on opposite sides of the hinge and physically coupled to the hinge, wherein a light transmitting area is defined in a portion of the supports (SP1, SP2); a foldable display panel disposed on a first surface of the support structure, and including a foldable display area corresponding to the hinge, and a plurality of display areas (DA1, DA2) disposed on opposite sides of the foldable display area; and an input sensor disposed in the light transmitting area of the support structure at a position spaced apart from the foldable display panel, wherein the light transmitting area corresponds to an opening defined in the support structure, characterized in that: a transparent insulating layer is disposed in the opening of the support structure, the input sensor is disposed on the transparent insulating layer, the transparent insulating layer is disposed between the input sensor and the foldable display panel when the foldable display panel is folded, and at least a portion of a sidewall of the opening of the support structure includes an inclined surface which is inclined with respect to a first direction perpendicular to the first surface of the support structure or to a second surface of the support structure facing the first surface, wherein a first width of the opening that is defined on a plane in an extension of the first surface of the support structure is greater than a second width of the opening that is defined on a plane in an extension of the second surface of the support structure. a transparent insulating layer is disposed in the opening of the support structure, the input sensor is disposed on the transparent insulating layer, the transparent insulating layer is disposed between the input sensor and the foldable display panel when the foldable display panel is folded, and at least a portion of a sidewall of the opening of the support structure includes an inclined surface which is inclined with respect to a first direction perpendicular to the first surface of the support structure or to a second surface of the support structure facing the first surface, wherein a first width of the opening that is defined on a plane in an extension of the first surface of the support structure is greater than a second width of the opening that is defined on a plane in an extension of the second surface of the support structure.