An amorphous silicon layer is deposited on a glass substrate via an underlayer insulating film, and further a light-emitting layer is inserted between the glass substrate and the underlayer insulating film in a partial region on the glass substrate. To measure light intensity distribution of laser light applied to the amorphous silicon layer, the laser light is applied to the light-emitting layer from the surface of a substrate to be treated. The light intensity distribution of the light emitted from the light-emitting layer is two-dimensionally imaged using an optical image pickup system from the back surface of the substrate to be treated, and measured using an image pickup device. The light intensity distribution of the laser light in the face to be treated is obtained from the light intensity distribution of the emission measured in this manner.