A laser beam having homogeneous intensity distribution is delivered without causing interference stripes of a laser to appear on an irradiation surface. A laser beam emitted from a laser oscillator passes through a diffractive optical element so that the intensity distribution thereof is homogenized. The beam emitted from the diffractive optical element then passes through a slit so that low-intensity end portions in a major-axis direction of the beam are blocked. Subsequently, the beam passes through a projecting lens and a condensing lens, so that an image of the slit is projected onto the irradiation surface. The projecting lens is provided so that the slit and the irradiation surface are conjugated. Thus, the irradiation surface can be irradiated with the laser having homogeneous intensity while preventing the diffraction by the slit.