A laser polycrystallization apparatus, comprising: a light source for emitting a laser beam; a diffraction grating for receiving the laser beam from the light source, changing a path and increasing a size of the received laser beam, and outputting the changed laser beam; a light splitting portion for splitting the changed laser beam received from the diffraction grating into split laser beams; 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, wherein 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, the diffraction grating is a transmission grating, and the laser beam from the light source passes through the diffraction grating and is converted into the changed laser beam, wherein the light splitting portion comprises: a first lens array located between the diffraction grating and the light superposition portion and comprising a plurality of first lenses, each of the first lenses having a semi-cylindrical shape, and a second lens array located between the first lens array and the light superposition portion and comprising a plurality of second lenses, each of the second lenses having a semi-cylindrical shape, wherein the plurality of first lenses is disposed on an incidence surface of the first lens array, wherein an emission surface of the first lens array has a planar shape, wherein the plurality of second lenses is disposed on an incidence surface of the second lens array, wherein an emission surface of the second lens array has a planar shape, and wherein the emission surface of the first lens array faces the incidence surface of the second lens array. a light source for emitting a laser beam; a diffraction grating for receiving the laser beam from the light source, changing a path and increasing a size of the received laser beam, and outputting the changed laser beam; a light splitting portion for splitting the changed laser beam received from the diffraction grating into split laser beams; 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, wherein 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, the diffraction grating is a transmission grating, and the laser beam from the light source passes through the diffraction grating and is converted into the changed laser beam, wherein the light splitting portion comprises: a first lens array located between the diffraction grating and the light superposition portion and comprising a plurality of first lenses, each of the first lenses having a semi-cylindrical shape, and a second lens array located between the first lens array and the light superposition portion and comprising a plurality of second lenses, each of the second lenses having a semi-cylindrical shape, wherein the plurality of first lenses is disposed on an incidence surface of the first lens array, wherein an emission surface of the first lens array has a planar shape, wherein the plurality of second lenses is disposed on an incidence surface of the second lens array, wherein an emission surface of the second lens array has a planar shape, and wherein the emission surface of the first lens array faces the incidence surface of the second lens array. a first lens array located between the diffraction grating and the light superposition portion and comprising a plurality of first lenses, each of the first lenses having a semi-cylindrical shape, and a second lens array located between the first lens array and the light superposition portion and comprising a plurality of second lenses, each of the second lenses having a semi-cylindrical shape, wherein the plurality of first lenses is disposed on an incidence surface of the first lens array, wherein an emission surface of the first lens array has a planar shape, wherein the plurality of second lenses is disposed on an incidence surface of the second lens array, wherein an emission surface of the second lens array has a planar shape, and wherein the emission surface of the first lens array faces the incidence surface of the second lens array.