A flexible device comprising: a main body comprising a folding unit; a flexible display fixed to a first surface of the main body; and a cover coupled to the main body such that the cover faces a second surface of the main body, wherein the second surface of the main body is opposite to the first surface of the main body, such that, when the main body is curved or folded, the cover is configured to move with respect to the second surface of the main body to compensate for a difference in elongation, which is generated when the main body is curved or folded wherein the flexible device further comprises a holding unit mounted in the main body and configured to cooperate with the folding unit to hold a curved or folded state of the main body, wherein the holding unit is disposed and configured to wrap at least a part of the folding unit, wherein the holding unit is further configured to generate a frictional force that holds the curved or folded state of the main body through friction with the folding unit, wherein the folding unit further comprises: a flexible material part; a folding member comprising a plurality of ribs arranged at regular intervals on the flexible material part and integrally fixed to the flexible material part to be folded; and wherein the folding member includes opposite ends, which are configured to slide within the main body when the main body is curved or folded, wherein the flexible material part is disposed between the cover and the folding member, and wherein the folding member is disposed to be concealed within the main body. a main body comprising a folding unit; a flexible display fixed to a first surface of the main body; and a cover coupled to the main body such that the cover faces a second surface of the main body, wherein the second surface of the main body is opposite to the first surface of the main body, such that, when the main body is curved or folded, the cover is configured to move with respect to the second surface of the main body to compensate for a difference in elongation, which is generated when the main body is curved or folded wherein the flexible device further comprises a holding unit mounted in the main body and configured to cooperate with the folding unit to hold a curved or folded state of the main body, wherein the holding unit is disposed and configured to wrap at least a part of the folding unit, wherein the holding unit is further configured to generate a frictional force that holds the curved or folded state of the main body through friction with the folding unit, wherein the folding unit further comprises: a flexible material part; a folding member comprising a plurality of ribs arranged at regular intervals on the flexible material part and integrally fixed to the flexible material part to be folded; and wherein the folding member includes opposite ends, which are configured to slide within the main body when the main body is curved or folded, wherein the flexible material part is disposed between the cover and the folding member, and wherein the folding member is disposed to be concealed within the main body. a flexible material part; a folding member comprising a plurality of ribs arranged at regular intervals on the flexible material part and integrally fixed to the flexible material part to be folded; and wherein the folding member includes opposite ends, which are configured to slide within the main body when the main body is curved or folded, wherein the flexible material part is disposed between the cover and the folding member, and wherein the folding member is disposed to be concealed within the main body.