A manufacturing method of a display device includes providing a display module including a display panel, a first flexible circuit board disposed at a first side edge of the display panel, a window disposed on the display panel, and an optical film disposed between the display panel and the window on the stage; aligning the display module such that the first side edge is disposed under the bonding unit; moving the position detection sensor along the first side edge of the display module to sense a first coating path; moving the resin supply unit along the sensed first coating path to coat a first filling agent between the window and the display panel; and moving the light irradiation unit along the sensed first coating path to cure the coated first filling agent to form a first filling layer.