A display device comprising: a flexible substrate including a pixel area, and a peripheral area surrounding the pixel area, the pixel area including a first area and a second area surrounding the first area, wherein the second area is a peripheral area of the first area formed outside the first area and has a shape enclosing the perimeter of the first area wherein the base layer is not provided and wherein the island patterns and bridge patterns are not provided; a base layer disposed on the pixel area, and comprising a plurality of island patterns on which respective pixels are provided and a plurality of bridge patterns coupling the adjacent island patterns to each other, the plurality of island patterns and the plurality of bridge patterns being disposed on the first area; a plurality electrically conducting lines disposed on the base layer and configured to measure a degree of elongation of the substrate, the said electrically conducting lines being provided on the islands and bridges and not being integrally formed such that they include first protrusions (RSL11, RSL21, RSL31) and second protrusions (RSL12, RSL22, RSL32) that extend towards each other in the second area; and signal lines coupled to the pixels and configured to drive the pixels, the said signal lines being provided on the plurality of bridge patterns; wherein, the plurality of first protrusions (RSL11, RS21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) are configured such that either: the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) come into contact with each other in the second area when the substrate is not elongated, and the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) do not come into contact with each other in the second area when the substrate is elongated, or the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) do not come into contact with each other in the second area when the substrate is not elongated, and the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL12, RSL22, RSL32) come into contact with each other in the second area when the substrate is elongated. a flexible substrate including a pixel area, and a peripheral area surrounding the pixel area, the pixel area including a first area and a second area surrounding the first area, wherein the second area is a peripheral area of the first area formed outside the first area and has a shape enclosing the perimeter of the first area wherein the base layer is not provided and wherein the island patterns and bridge patterns are not provided; a base layer disposed on the pixel area, and comprising a plurality of island patterns on which respective pixels are provided and a plurality of bridge patterns coupling the adjacent island patterns to each other, the plurality of island patterns and the plurality of bridge patterns being disposed on the first area; a plurality electrically conducting lines disposed on the base layer and configured to measure a degree of elongation of the substrate, the said electrically conducting lines being provided on the islands and bridges and not being integrally formed such that they include first protrusions (RSL11, RSL21, RSL31) and second protrusions (RSL12, RSL22, RSL32) that extend towards each other in the second area; and signal lines coupled to the pixels and configured to drive the pixels, the said signal lines being provided on the plurality of bridge patterns; wherein, the plurality of first protrusions (RSL11, RS21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) are configured such that either: the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) come into contact with each other in the second area when the substrate is not elongated, and the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) do not come into contact with each other in the second area when the substrate is elongated, or the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) do not come into contact with each other in the second area when the substrate is not elongated, and the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL12, RSL22, RSL32) come into contact with each other in the second area when the substrate is elongated. the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) come into contact with each other in the second area when the substrate is not elongated, and the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) do not come into contact with each other in the second area when the substrate is elongated, or the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL21, RSL22, RSL32) do not come into contact with each other in the second area when the substrate is not elongated, and the plurality of first protrusions (RSL11, RSL21, RSL31) and the plurality of second protrusions (RSL12, RSL22, RSL32) come into contact with each other in the second area when the substrate is elongated.