A display device comprising: a display module including: a first folding area (FA1) extending in a second direction (DR2); a first non-folding area (NFA1) located on a first side of the first folding area (FA1) in a first direction (DR1) intersecting the second direction (DR2); a second non-folding area (NFA2) located on a second side of the first folding area (FA1) in the first direction (DR1); a second folding area (FA2) extending in the first direction (DR1); a third non-folding area (NFA3) located on a first side of the second folding area (FA2) in the first direction (DR1); a fourth non-folding area (NFA4) located on a second side of the second folding area (FA2) in the second direction (DR2), a plurality of main plates disposed under the display module , and a first gear unit disposed in a portion of the second folding area (FA2) which does not overlap the first folding area (FA1), wherein the display module includes a first surface and a second surface opposite to the first surface, the first surface being a display surface, and in an out-folding operation state, the display device is folded with respect to the second folding area (FA2) such that the second surface in the third non-folding area (NFA3) and the second surface in the fourth non-folding area (NFA4) face each other, wherein the first gear unit includes an extension part extending in the first direction (DR1), and at least one joint part extending in the second direction (DR1) from the extension part , wherein the at least one joint part includes a plurality of joint parts , and the plurality of joint parts is disposed in the plurality of main plates and overlaps the plurality of main plates , wherein an overlap length of the plurality of main plates and the at least one joint part in an unfolded state of the display device is smaller than an overlap length of the plurality of main plates and the at least one joint part in the out-folding operation state of the display device . a first folding area (FA1) extending in a second direction (DR2); a first non-folding area (NFA1) located on a first side of the first folding area (FA1) in a first direction (DR1) intersecting the second direction (DR2); a second non-folding area (NFA2) located on a second side of the first folding area (FA1) in the first direction (DR1); a second folding area (FA2) extending in the first direction (DR1); a third non-folding area (NFA3) located on a first side of the second folding area (FA2) in the first direction (DR1); a fourth non-folding area (NFA4) located on a second side of the second folding area (FA2) in the second direction (DR2), a plurality of main plates disposed under the display module , and a first gear unit disposed in a portion of the second folding area (FA2) which does not overlap the first folding area (FA1), wherein the display module includes a first surface and a second surface opposite to the first surface, the first surface being a display surface, and in an out-folding operation state, the display device is folded with respect to the second folding area (FA2) such that the second surface in the third non-folding area (NFA3) and the second surface in the fourth non-folding area (NFA4) face each other, wherein the first gear unit includes an extension part extending in the first direction (DR1), and at least one joint part extending in the second direction (DR1) from the extension part , wherein the at least one joint part includes a plurality of joint parts , and the plurality of joint parts is disposed in the plurality of main plates and overlaps the plurality of main plates , wherein an overlap length of the plurality of main plates and the at least one joint part in an unfolded state of the display device is smaller than an overlap length of the plurality of main plates and the at least one joint part in the out-folding operation state of the display device . <EOS>