Abstract: A laser annealing device (10) includes a laser oscillator (12), radiating a pulsed laser light beam of a preset period, and an illuminating optical system (15) for illuminating a pulsed laser light beam to an amorphous silicon film (1). The illuminating optical system (15) manages control for moving a laser spot so that a plural number of light pulses will be illuminated on the same location on the amorphous silicon film (1). The laser oscillator (12) radiates a laser light beam of a pulse generation period shorter than the reference period. The reference period is a time interval as from the radiation timing of illumination of a pulsed laser light beam on the surface of the film (1) until the timing of reversion of the substrate temperature raised due to the illumination of the laser light beam to the original substrate temperature.