Patent ID: 7023597

Claim:
An optical scanner that scans a light beam on a surface to be scanned in a main scanning direction and a sub scanning direction orthogonal to the main scanning direction, comprising: a light source; a rotary polyhedral mirror that scans a light beam from the light source; an image forming optical system that is disposed between the light source and the rotary polyhedral mirror and forms a line image larger in size than a width in the main scanning direction of one reflecting surface of the rotary polyhedral mirror on the reflecting surface; and a curved surface mirror that is disposed between the rotary polyhedral mirror and the surface to be scanned, wherein the light source, the image forming optical system, the rotary polyhedral mirror and the curved surface mirror are arranged respectively in different positions in the sub scanning direction, a light beam from the image forming optical system is incident on the reflecting surface of the rotary polyhedral mirror obliquely with respect to a first plane that includes a normal of the reflecting surface and is parallel to the main scanning direction, and a light beam reflected off the rotary polyhedral mirror is incident on the curved surface mirror obliquely with respect to a second plane that includes a normal at a vertex of the curved surface mirror and is parallel to the main scanning direction.