Patent ID: 8896649

Claim:
An optical scanning device comprising: a light source unit; a light deflecting unit that deflects a light beam emitted from the light source unit; and a scanning optical device that focuses the light beam deflected by the light deflecting unit on a scanned surface, wherein the scanning optical device is provided in a direction in which there is a sound pressure level of a noise caused by rotation of a rotating polygon mirror included in the light deflecting unit, wherein when a direction parallel to a scanning direction of the light beam that passes through a rotation center of the rotating polygon mirror included in the light deflecting unit and scans the scanned surface is set as a Y axis; a direction that is perpendicular to a rotating shaft of the rotating polygon mirror is set as an X axis; two light shielding members provided such that at least a portion thereof is present in an area surrounded by a circumscribed circle of the rotating polygon mirror, by a first straight line that is perpendicular to the Y axis and is tangential to the circumscribed circle, and by a first optical axis of the light beam emitted from the light source unit are denoted by a first light shielding member and a second light shielding member; other two light shielding members provided such that at least a portion thereof is present in an area surrounded by the circumscribed circle of the rotating polygon mirror, by a second straight line that is perpendicular to the Y axis and is tangential to the circumscribed circle, and by a second optical axis of the light beam emitted from the light source unit and deflected by the light deflecting unit are denoted by a third light shielding member and a fourth light shielding member; a distance, in the X-axis direction, between the first light shielding member and the second light shielding member is denoted by L 1 ; a distance, in the Y-axis direction, between the first light shielding member and the third light shielding member is denoted by L 2 ; and a distance, in the Y-axis direction, between the second light shielding member and the fourth light shielding member is denoted by L 3 , one of a relation of L 1 <L 2 and a relation of L 1 <L 3 is satisfied.