A laser crystallization apparatus and method for crystallizing a semiconductor thin film while monitoring at a high spatial and temporal resolution in real time. In a laser crystallization apparatus comprising a crystallizing optical system which irradiates a semiconductor thin film with a pulse laser light having an intensity distribution to melt and to crystallize the thin film in a manner to grow grains laterally, the apparatus comprises an illumination light source provided out of an optical path of the laser, an illumination optical system including annular optical elements which provides the optical path of the laser light in a central portion and guides the illumination light to the thin film, and an observing optical system which magnifies the illumination light transmitted through the thin film, picks up an image of the grains growing laterally, and displays the image.