A device for bonding a window includes a chamber having an internal space, a display panel fixing unit in the chamber and including a first curved surface, the first curved surface being configured to attach to a flexible display panel, a window fixing unit in the chamber and including a second curved surface, at least part of the window fixing unit including an ultraviolet transmitting material, the second curved surface facing the first curved surface and being complementary with the first curved surface, and the second curved surface being configured to attach to a window, and an ultraviolet irradiating unit on the window fixing unit, the ultraviolet irradiating unit being configured to irradiate ultraviolet light through the window fixing unit toward the first curved surface of the display panel fixing unit.