A laser annealing device includes a stage, a laser generator, and a reflective member. The stage supports a substrate with a thin film formed thereon to be processed, and may be moved in a first direction at a set or predetermined speed. The laser generator irradiates a first area of the thin film with a laser beam while the stage is moved. The reflective member reflects a part of the laser beam, which is reflected from the first area of the thin film, to a second area of the thin film. The first area and the second area are spaced apart from each other.