A laser annealing device includes a laser beam source, a laser beam irradiating optical system that irradiates a treatment area of a treatment object substrate with a laser beam emitted from the laser beam source, an illumination light source that emits illumination light in a visible light region, an illumination optical system that irradiates the treatment area with light emitted from the illumination light source, and a spectral detector that detects light in the visible light region that has been reflected by the treatment area in which an annealing treatment has been performed with the laser beam, and outputs spectral characteristics of the light.