A laser polycrystallization apparatus including: a light source for emitting a laser beam; a diffraction grating for receiving the laser beam from the light source, changing a path and a magnitude of the received laser beam, and outputting the changed laser beam; a light split portion for splitting the laser beam received from the diffraction grating; and a light superposition portion for superposing the split laser beams received from the light split portion and irradiating the superposed split laser beams to a substrate. An angle between the laser beam irradiated to an incidence surface of the diffraction grating from the light source and a line substantially perpendicular to an emission surface of the diffraction grating is an acute angle.