There are provided a crystallization method which can design laser beam having a light intensity and a distribution optimized on an incident surface of a substrate, form a desired crystallized structure while suppressing generation of any other undesirable structure area and satisfy a demand for low-temperature processing, a crystallization apparatus, a thin film transistor and a display apparatus. When crystallizing a non-single-crystal semiconductor thin film by irradiating laser beam thereto, irradiation light beam to the non-single-crystal semiconductor thin film have a light intensity with a light intensity distribution which cyclically repeats a monotonous increase and a monotonous decrease and a light intensity which melts the non-single-crystal semiconductor. Further, at least a silicon oxide film is provided on a laser beam incident surface of the non-single-crystal semiconductor film.