A laser annealing apparatus used in a crystallization process of an amorphous silicon thin film. The laser annealing apparatus includes a laser beam generation unit generating a laser beam, an optical system dividing the laser beam into a plurality of linear laser beams and including a focusing lens focusing the linear laser beams and projecting the focused linear laser beam on a substrate to be processed, and a focusing lens adjustment device adjusting a perpendicular distance and a rotation angle of the focusing lens relative to the substrate.