A light scanning apparatus including a semiconductor laser which emits a light beam having a wavelength equal to or less than 450 nm, an incidence optical system which makes the light beam, emitted from the semiconductor laser, incident on a deflector for scanning in deflection, an imaging optical system which images the light beam scanned in deflection by the deflector to a surface to be scanned, a light intensity detector which detects fluctuations in spectral transmittances of the incidence optical system and of the imaging optical system, which are caused as a concomitant of a fluctuation in wavelength of the light beam which is emitted from the semiconductor laser and passes through the incident optical system and the imaging optical system, and an automatic power controller which automatically controls a light emission output of the semiconductor laser on the basis of a detection value detected by the light intensity detector.