Image forming apparatus with fan configured for dust-resistant cooling of optical scanning unit

An image forming apparatus for forming an image on a recording material, comprising:

• a photosensitive member;
• an optical scanning unit configured to scan said photosensitive member with a light beam in accordance with image information, wherein said optical scanning unit includes a light source configured to emit the light beam in accordance with the image information, a rotatable polygonal mirror configured to deflect the light beam emitted from said light source, an optical box supporting said rotatable polygonal mirror, and a cover covering an opening of said optical box;
• and
• a fan configured to cool an inside of said image forming apparatus,
• wherein said fan is provided so that air from said fan directly impinges on said optical box of said optical scanning unit,
• wherein as seen in a direction perpendicular to a rotational axis of said rotatable polygonal mirror, a rib extending from a plate supporting said rotatable polygonal mirror of said optical box toward a cover side is provided at a portion of said optical box in a neighborhood of a light beam emitting port of said optical scanning unit,
• wherein said optical box is provided with an extended portion extended from said rib in a light beam emitting direction, and
• wherein said fan is provided on a side upstream of said emitting port with respect to the light beam emitting direction, and a direction of the air impinging on said optical box by said fan is a direction from an upstream side toward a downstream side with respect to the light beam emitting direction.