A laser annealing apparatus comprises a laser oscillator having a Q switching action, one or a plurality of partially reflective mirrors for split a laser beam emitted from the laser oscillator into a plurality of laser beams, a plurality of optical fibers which respectively transmit the plurality of laser beams split by the partially reflective mirrors, and whose respective emission ends are arranged linearly in one direction, a first optical system for synthesizing and homogenizing the plurality of laser beams emitted from the optical fibers, and a second optical system for focusing the laser beam emitted from the first optical system on the work piece surface as a rectangular laser beam whose beam shape is long in the lateral direction and short in the longitudinal direction. As a result, laser power transmission by means of slender optical fibers is possible even in cases in which a green laser such as the second harmonic of an Nd:YAG laser having a Q switching action or the like is used as a heating light source. Accordingly, a compact laser annealing apparatus that has a high-quality working performance and does not require a laser amplifier or high-frequency generating apparatus can be obtained.