A flexible display device includes a substrate including a non-bending area and a bending area adjacent to the non-bending area, and a crack prevention pattern disposed in the bending area. The bending area includes a first area having a first stress when bending, a second area having a second stress less than the first stress when bending, and a third area having a third stress less than the second stress when bending. The crack prevention pattern includes a plurality of crack prevention lines. The number of the crack prevention lines in the first area is greater than the number of the crack prevention lines in the third area.