Provided are a laser irradiation device and a laser irradiation method, which are suitable for a liquid crystal display device. The laser irradiation device comprises a semiconductor laser element group (1A) having a plurality of semiconductor laser elements (1) arranged therein for emitting laser beams of a wavelength of 370 nm to 480 nm, optical fibers (2) for transmitting the laser beams emitted from the semiconductor laser elements (1), a straight bundle (3) for holding the optical fibers (2) straight, an optical adjustor (4) for shaping the laser beams outputted from the optical fibers held by the straight bundle (3), into a linear shape and for smoothing the top of the laser intensity distribution thereby to output the smoothed laser beams, and an objective lens (5) for condensing the laser beams outputted from the optical adjustor (4), as a linear laser spot on an object. The semiconductor laser element group (1A) has a total irradiation output value of 6 W to 100 W.