A method for forming a crystallized semiconductor layer includes preparing a non-single-crystal semiconductor layer in which at least one crystal seed is formed, and irradiating with an energy ray the non-single-crystal semiconductor layer having the crystal seed formed therein to allow a crystal to laterally grow from the crystal seed in the non-single-crystal semiconductor layer, irradiation of the energy ray is carried out by positioning to at least a part of the crystal seed an area having a minimum intensity value of the energy ray, the energy ray having a confirmation that an area having a maximum intensity value of the energy ray is continuously reduced to the area having the minimum intensity value in an irradiated surface.