A crystallization apparatus is provided. In the crystallization apparatus, a light intensity distribution formed by a light modulation device or a metal aperture and transferred to a processed substrate can be visualized. The crystallization apparatus has an ultraviolet (UV) irradiation system and a visible light irradiation system. The UV irradiation system irradiates pulses of laser beam in the UV range to the processed substrate. The visible light irradiation system continuously irradiates a visible light laser beam on the same irradiated region on the processed substrate. In a melted region resulted from the uniform irradiation of the laser beam in the UV range, the light intensity distribution of the visible laser beam is used to form crystal growth. The crystallization apparatus irradiates pulses of the laser beam in the UV range to melt the processed substrate, and continuously irradiates the visible light laser beam to crystallize the processed substrate.