It is an object of the present invention to provide a laser irradiation apparatus being able to crystallize the semiconductor film homogeneously while suppressing the variation of the crystallinity in the semiconductor film and the unevenness of the state of the surface thereof. It is another object of the present invention to provide a method for manufacturing a semiconductor device using the laser irradiation apparatus which can suppress the variation of on-current, mobility, and threshold of TFT, and to further provide a semiconductor device manufactured with the manufacturing method.A method for manufacturing a semiconductor device comprising the steps of adding the first noble gas to the semiconductor film formed over the insulating surface with the ion doping method and irradiating the semiconductor film with the first noble gas added therein with the laser light in an atmosphere of second noble gas, wherein the magnetic field is applied to the semiconductor film with the first noble gas added when the laser light is irradiated.