Abstract: An optical sound recording system of modified variable area type, wherein a light beam, preferably a laser beam, is pulse-width modulated in response to sound signals and deflected at a high frequency beyond audible range and then recorded on a sound track of cinema film. The pulse-width modulation of the light beam is performed in such a manner that a carrier wave having the same frequency, phase, and wave form to those of the deflection of the light beam and being clipped on both sides of amplitude by a pair of sound signals polarized inversely with each other and biased positively and negatively is used for gating the light beam. Consequently a high quality optical sound recording system unrelated to the carrier waveform used for the pulse-width modulation can be realized.