Patent ID: 6847474

Claim:
A ghost image preventing method for preventing a reflected beam from acting as ghost light in an optical scanning device, comprising: deflecting a beam from a light source by a light deflector having a deflection reflective surface rotating or swinging; condensing the deflected light toward a surface to be scanned by a scanning imaging optical system; forming a beam spot on the surface to be scanned; and performing optical scanning of the surface to be scanned, wherein a transparent parallel plate closing a window provided in a housing containing the light deflector for causing the beam from the light source to be incident on the deflection reflective surface, and causing the beam reflected by the deflection reflective surface to exit from the housing is inclined with respect to a direction perpendicular to a deflection scanning plane, the scanning imaging optical system includes at least one rectangular lens, and a relative positional relationship between said at least one rectangular lens and the parallel plate is set such that the beam reflected by the parallel plate is prevented from being incident on a side-end surface in a sub-scanning direction of the at least one rectangular lens.