Patent ID: 8207997

Claim:
An optical scanning apparatus, comprising: a first scanning unit and a second scanning unit facing each other with a rotational polygon mirror interposed therebetween in a sub-scanning section, the first scanning unit and the second scanning unit each including: an incident optical system in which a light beam emitted from a light source is made incident on a deflecting surface of the rotational polygon mirror; and an imaging optical system including an imaging optical element configured to cause the light beam, deflected for scanning on the deflecting surface of the rotational polygon mirror, form an image on a surface to be scanned, wherein the light beam that enters the deflecting surface of the rotational polygon mirror enters obliquely with respect to a normal of the deflecting surface of the rotational polygon mirror in the sub-scanning section, wherein the first scanning unit includes an undesirable-light blocking member configured to block an undesirable light reflected on an optical surface of the imaging optical element of the second scanning unit to travel toward the surface to be scanned of the first scanning unit, wherein the following condition is satisfied: rp<L≦A/ 2 where rp denotes a circumcircle radius of the rotational polygon mirror, L denotes a distance from a rotational center of the rotational polygon mirror to the undesirable-light blocking member of the first scanning unit in a direction of an optical axis of the imaging optical system, and A denotes a length of a drive circuit substrate for driving the rotational polygon mirror in the direction of the optical axis of the imaging optical system, wherein the undesirable-light blocking member is integrally formed with an optical box in which the drive circuit substrate is fixed, and wherein the second scanning unit includes an undesirable-light blocking member configured to block an undesirable light reflected on an optical surface of the imaging optical element of the first scanning unit to travel toward a surface to be scanned of the second scanning unit, wherein the following condition is satisfied: A/ 2 <L′ where L′ denotes a distance from the rotational center of the rotational polygon mirror to the undesirable-light blocking member of the second scanning unit in the direction of the optical axis of the imaging optical system, and wherein an opening width of the undesirable-light blocking member of the first scanning unit in a sub-scanning direction is narrower than an opening width of the undesirable-light blocking member of the second scanning unit in the sub-scanning direction.