According to an embodiment, an apparatus for manufacturing a display device includes a stage on which a target substrate is mounted, and a suction unit positioned above the stage. The suction unit includes a main body including an outer box with top and bottom openings and an inner cup disposed in the outer box, a light emitting unit disposed on at least one inner surface of the outer box, the light emitting unit providing light, and a light receiving unit disposed opposite to the light emitting unit, and disposed on at least one inner surface of the outer box, the light receiving unit receiving the light provided from the light emitting unit.