Disclosed herein is an apparatus for processing a substrate that forms a hole in a substrate while reducing a burr in the hole so that a module device can be inserted into the hole to reduce the thickness of a display device, and the display device using the apparatus. The apparatus for processing the substrate comprises a body configured to operably be rotatable, and a cylindrical cutting tip at an end of the body. The bottom surface of the cutting tip is in an acute angle with respect to a contact surface of the substrate to allow formation of a groove at the substrate.