An optical scanning apparatus includes a deflecting device for scanning and deflecting a light beam, a first optical member onto which reflected light from the deflecting device is incident, a wall disposed between the first optical member and the deflecting device, a mirror that reflects the light beam having passed through the first optical member, a second optical member disposed above the deflecting device to guide and form an image of reflected light from the mirror on a surface to be scanned, a supporting member supporting the second optical member and having at least one bent portion, and a housing. The bent portion of the supporting member is disposed above the deflecting device in a position nearer to the deflecting device than the wall face in a direction perpendicular to the deflecting face of the deflecting device so that a flow of air produced by the deflecting device is branched.