A laser irradiation apparatus comprising an optical system and a plurality of semiconductor laser devices, wherein the optical system comprises an optical fiber bundle comprising a bundle of a plurality of optical fibers, wherein one end of the optical fiber bundle forms an incident side bundle end at which light incident ends of individual optical fibers are arranged, and the other end forms an emission side bundle end at which light emission ends of individual optical fibers are arranged, and the optical fiber bundle further comprising: at the emission side bundle end, an optical deflection unit that deflects at least two light beams toward different directions, respectively, such that the at least two light beams emitted from respective light emission ends of at least two optical fibers (2a, 2b) out of the plurality of optical fibers overlap each other on at least one cross section that is at rear on an optical path of the emission side bundle end and are then scattered, wherein the bundle of the plurality of optical fibers includes a center optical fiber and at least one peripheral optical fiber that is adjacent to the center optical fiber, and the optical fiber bundle is configured such that a light beam emitted from the center optical fiber travels straight along an optical axis of the center optical fiber, and a light beam emitted from the peripheral optical fiber is deflected toward a light beam emitted from the center optical fiber, and wherein the plurality of semiconductor laser devices are arranged on an incident end side of the optical fiber bundle, wherein the optical fiber bundle is configured such that laser lights generated by the plurality of semiconductor laser devices separately enter the at least two optical fibers (2a, 2b) of the optical fiber bundle, wherein the optical fiber bundle is configured such that a light beam emitted from the peripheral optical fiber is deflected toward the optical axis of the center fiber at an angle that is larger than a beam divergence of the light beam and the at least two light beams completely overlap each other before spreading to the diameter of the fiber bundle, two lenses are arranged at the rear on the optical path of the optical fiber bundle, and the optical fiber bundle is configured such that the at least two light beams overlap each other on the at least two cross sections at the rear on an optical path at the emission side bundle end, characterized in that the plurality of semiconductor laser devices generate laser light having peak wavelengths that are separated from each other by more than or equal to half width at half maximum of spectral line width of the at least two light beams, and the optical fiber bundle is configured such that the at least two light beams are incoherent to each other. wherein the plurality of semiconductor laser devices are arranged on an incident end side of the optical fiber bundle, wherein the optical fiber bundle is configured such that laser lights generated by the plurality of semiconductor laser devices separately enter the at least two optical fibers (2a, 2b) of the optical fiber bundle, wherein the optical fiber bundle is configured such that a light beam emitted from the peripheral optical fiber is deflected toward the optical axis of the center fiber at an angle that is larger than a beam divergence of the light beam and the at least two light beams completely overlap each other before spreading to the diameter of the fiber bundle, two lenses are arranged at the rear on the optical path of the optical fiber bundle, and the optical fiber bundle is configured such that the at least two light beams overlap each other on the at least two cross sections at the rear on an optical path at the emission side bundle end, characterized in that the plurality of semiconductor laser devices generate laser light having peak wavelengths that are separated from each other by more than or equal to half width at half maximum of spectral line width of the at least two light beams, and the optical fiber bundle is configured such that the at least two light beams are incoherent to each other.