Optical scanning device, image reading device provided with this, image forming device, and photographing device

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.