A method of manufacturing a flexible display device includes a first step of providing a three-dimensional cover window having a flat portion, and a curved portion that is bent in a third direction intersecting a first direction of the flat portion while extending to a second direction intersecting the first direction at both sides of the first direction, and a second step of attaching by a line contact at least one of an adhesive film, a touch panel, and a flexible display panel that are stacked at an inner surface of the cover window.