A sequential lateral solidification device, for enhancing optical characteristics of the device and for preventing damage caused by an ablation of a crystallization thin film, is disclosed. The device includes a laser light source generating a laser beam, a projection lens focusing the laser beam generated from the laser light source onto a substrate, a laser beam splitter between the projection lens and the substrate that passes the laser beam generated from the laser light source to irradiate the substrate and that blocks the laser beam reflected back from the substrate towards the projection lens, and a stage having the substrate mounted thereon.