A display device comprising: a housing; a display portion comprising a display panel and a module cover; a roller positioned in the housing; an operating portion attached to one end of the display portion and configured to wind or unwind the display portion to change a state of the display portion between a first state where the display portion is kept wound around the roller, and a second state where the display portion is kept unwound from the roller and exposed out of the housing; wherein the operating portion comprises: a motor assembly positioned in the housing; supports for supporting both sides of a top bar, each support including a lower link having one end connected to the motor assembly and an upper link having one end connected to the top bar coupled to an upper part of the display portion, the upper link and the lower link being connected by a hinge, and the motor assembly being configured to pivot the lower link to allow the top bar to ascend or descend; the display device further comprising: a roller hub attached to a center axis of the roller and configured to rotate together with the roller; a constant spring spaced apart from the roller hub and configured to rotate in the opposite direction to the roller hub during a transition from the first or second state to the other state; and a transmission belt wound around the constant spring and wound around the roller hub, wherein the roller hub is configured to rotate together with the roller in a first direction, which is a rotational clockwise or counter-clockwise direction, wherein the constant spring has a certain amount of torque in a second direction which is opposite to the first direction, wherein the display portion and the transmission belt are wound in opposite directions, such that, as the display portion and the roller hub rotate in the first direction, the transmission belt is unwound from the roller hub and the display portion is wound around the roller. a housing; a display portion comprising a display panel and a module cover; a roller positioned in the housing; an operating portion attached to one end of the display portion and configured to wind or unwind the display portion to change a state of the display portion between a first state where the display portion is kept wound around the roller, and a second state where the display portion is kept unwound from the roller and exposed out of the housing; wherein the operating portion comprises: a motor assembly positioned in the housing; supports for supporting both sides of a top bar, each support including a lower link having one end connected to the motor assembly and an upper link having one end connected to the top bar coupled to an upper part of the display portion, the upper link and the lower link being connected by a hinge, and the motor assembly being configured to pivot the lower link to allow the top bar to ascend or descend; the display device further comprising: a roller hub attached to a center axis of the roller and configured to rotate together with the roller; a constant spring spaced apart from the roller hub and configured to rotate in the opposite direction to the roller hub during a transition from the first or second state to the other state; and a transmission belt wound around the constant spring and wound around the roller hub, wherein the roller hub is configured to rotate together with the roller in a first direction, which is a rotational clockwise or counter-clockwise direction, wherein the constant spring has a certain amount of torque in a second direction which is opposite to the first direction, wherein the display portion and the transmission belt are wound in opposite directions, such that, as the display portion and the roller hub rotate in the first direction, the transmission belt is unwound from the roller hub and the display portion is wound around the roller. a roller hub attached to a center axis of the roller and configured to rotate together with the roller; a constant spring spaced apart from the roller hub and configured to rotate in the opposite direction to the roller hub during a transition from the first or second state to the other state; and a transmission belt wound around the constant spring and wound around the roller hub, wherein the roller hub is configured to rotate together with the roller in a first direction, which is a rotational clockwise or counter-clockwise direction, wherein the constant spring has a certain amount of torque in a second direction which is opposite to the first direction, wherein the display portion and the transmission belt are wound in opposite directions, such that, as the display portion and the roller hub rotate in the first direction, the transmission belt is unwound from the roller hub and the display portion is wound around the roller.