PURPOSE: To provide an optical scanning device which can form an image with high resolution although the device is low in cost and compact.

CONSTITUTION: The optical scanning device 1 is mounted on a laser printer and provided with two laser light sources (laser diodes) 11a and 11b which emit light according to data on an image to be printed, two polygon mirrors 13a and 13b, a scanner motor 15 which drives and rotates polygon mirrors 13a and 13b, an Fθ lens 17 through which deflected beams from the polygon mirrors 13a and 13b pass, and a concave mirror 21 which converges the laser beam on a drum-shaped photosensitive body 19. The two polygon mirrors 13a and 13b are fixed on the rotary shaft 15a of the scanner motor 15, one over the other, and shifted by a half (30°) as large as the center angle (60°) of a regular hexagon from each other in the direction of rotation on the rotary shaft 15a.