Patent ID: 7791774

Claim:
A scanning optical apparatus, comprising: a light source for outputting a beam light; a polygon mirror for reflecting said beam light outputted from said light source and then transforming said beam light into a scanning light on a prescribed scanning surface as rotating about a rotational axis along a sub scanning direction; and a lens system provided on a light path of said beam light in between said polygon mirror and said scanning surface, said lens system comprising a curvature changing lens as a lens to the side of said polygon mirror which monotonically changes its curvature of a cross section in said sub scanning direction of an incident surface and/or an outputting surface of said beam light with respect to a distance from a predetermined center position in a main scanning direction, as a scanning direction of said beam light, intersecting with said sub scanning direction, and a decentered lens as a lens to the side of said scanning surface arranged with its lens axis inclined and/or displaced with respect to a light axis of said beam light, said beam light outputted from said light source falling on said polygon mirror at an angle up to ±2° with respect to a cross section perpendicular to said sub scanning direction.