a laser beam scanning device is comprised of a laser beam source for emitting a laser beam , a polygon mirror rotatable for reflecting the laser beam to deflect the same linearly in primary scanning direction and a main motor for rotating the polygon mirror . an optically converging system converges the laser beam reflected from the polygon mirror onto a photosensitive medium . a secondary scanning system includes a driving source having a pulse motor for shifting the laser beam relative to the photosensitive medium in secondary scanning direction substantially perpendicular to the primary scanning direction to thereby scan the laser beam two - dimensionally on the photosensitive medium . a controlling circuit produces a common clock signal for controlling and driving the main motor and the pulse motor according to the common clock signal .