A laser irradiation apparatus for irradiating a laser beam to a semiconductor layer including a plurality of pixel areas, the apparatus includes a laser generator generating the laser beam, and an optical switching unit time-dividing the laser beam generated from the laser generator and transmitting a plurality of time-divided laser beams to a plurality of optical systems. The apparatus includes a first optical system of the plurality of optical systems that receives a first time-divided laser beam and irradiates a first laser slit beam along a first irradiation direction, and a second optical system of the plurality of optical systems that receives a second time-divided laser beam and irradiates a second laser slit beam along a second irradiation direction that is parallel with the first irradiation direction. The first laser slit beam and the second laser slit beam crystallize partial areas at a same location in the respective pixel areas.