a laser scanning device for use with an image forming apparatus , including an optical housing , a light source installed in the optical housing to generate a laser beam , a deflection unit to deflect the laser beam emitted from the light source , a focusing lens to focus the laser beam deflected by the deflection unit onto a laser scanning surface , a reflective mirror to change the path of the laser beam and thereby , scan the laser beam onto a position of the laser scanning surface , and a mirror assembly unit to diversify installation angles of the reflective mirror to facilitate an assembly thereof .