In an optical scanning device using two polygon mirrors, the present
invention achieves both a simplification of the device and a reduction of
vibrations. An optical scanning device is provided with a first optical
system including a polygon mirror and a second optical system including a
polygon mirror. The polygon mirror provided in the first optical system
and the polygon mirror provided in the second optical system are
configured such that they rotate in mutually opposite directions.
Further, the optical scanning device is provided with one BD sensor for
detecting laser beams that are scanned with the polygon mirrors. Slits
with mutually different widths are arranged between the BD sensor and the
respective polygon mirrors of the first and second optical systems.