An apparatus for manufacturing a display device includes: a stage on which a substrate to be processed is supported, the substrate to be processed including a first alignment layer of the display device; an optical system facing the substrate to be processed which is supported on the stage, the optical system including a light source which irradiates ultraviolet rays to the substrate to be processed; and a mask which is interposed between the light source and the substrate to be processed which includes the first alignment layer of the display device. The mask defines: a transmitting portion thereof through which the ultraviolet rays irradiated from the light source are transmitted to the first alignment layer of the substrate to be processed, and a blocking portion thereof which blocks transmission of the ultraviolet rays irradiated from the light source to the substrate to be processed.