An apparatus for stabilizing a laser beam to be used for exposure in an image-reproducing apparatus wherein said beam is suitably controlled by image signals obtained from the scanning of the original beam as modulated. A laser beam, after being suitably modulated by an ultrasonic light modulator, is branched out by a half mirror into two beams, one of which is to be used for exposing a photosensitive material and the other is used as a negative feedback signal. This feedback signal is then added to an image signal so that a linearity between exposing beam and image signals are greatly improved. Further, by improving the linearity of exposing beam, the stability of the exposing beam is simultaneously improved.