A maskless exposure device includes an exposure head including a digital micro-mirror device and an exposure source, the digital micro-mirror device being configured to reflect a source beam outputted from the exposure source to a substrate and a system controller configured to control the digital micro-mirror device by using a graphic data system file. The graphic data system file includes data regarding patterns to be formed on the substrate. A pattern extending in a direction parallel to a scan direction of the exposure head includes a first pattern portion having a first width that is greater than a target width and a second pattern portion alternately disposed with the first pattern portion and having a second width that is less than the target width.