A laser crystallizing apparatus includes a laser generator that generates an incident laser beam that includes a P polarization component and an S polarization component, an optical system that converts the incident laser beam to generate an emitted laser beam, and a stage on which is mounted a target substrate with a target thin film which is laser-crystallized by being irradiated by the emitted laser beam. The optical system includes at least one half wave plate (HWP) that shifts a polarization axis direction of the incident laser beam received from the laser generator, at least one mirror that fully reflects the laser beam, and at least one polarization beam splitter (PBS) which reflects a part of the laser beam and transmits the other part of the laser beam.