In an optical scanning apparatus, when air flow from a deflecting device is suppressed by a shielding member such as a transparent member, an image of a light beam is not formed at a predetermined position. In view of this, a first wall portion having a wall surface shaped concentrically with a center axis of a deflecting device is provided on an optical path directed from a laser light source toward the deflecting device. By providing at least the first wall portion having laser beam passing portions as openings passing through the wall surface of the first wall portion and providing a second wall portion connected to the first wall portion to define a closed surface except for the laser beam passing portions, warm air flow directed from the deflecting device to the laser light source is blocked.