A crystallization method includes wavefront-dividing an incident light beam into a plurality of light beams, condensing the wavefront-divided light beams in a corresponding phase shift portion of a phase shift mask or in the vicinity of the phase shift portion to form a light beam having an light intensity distribution of an inverse peak pattern in which a light intensity is minimum in a point corresponding to the phase shift portion of the phase shift mask, and irradiating a polycrystalline semiconductor film or an amorphous semiconductor film with the light beam having the light intensity distribution to produce a crystallized semiconductor film.