Scanning type image forming apparatus having the same containing scanning mirror in a space sealed by first and second optical members and the housing, the second optical member includes five surfaces

An image forming apparatus which scans a surface to be scanned with beam to form an image on the surface to be scanned, comprising:

• a scanning device including a scanning mirror swinging about a swinging center, an elastic supporting portion for supporting the scanning mirror, and a supporting base for supporting the elastic supporting portion;
• a housing for containing the scanning device therein;
• a light source;
• a first optical member for directing a beam emitted from the light source to the scanning mirror disposed in the housing, the first optical member having a condensing function;
• a second optical member for directing the beam reflected by the scanning mirror to the surface to be scanned;
• and
• an emergence window disposed between the second optical member and the surface to be scanned,
• wherein the first optical member, the scanning mirror and the second optical member are optical members different from one another,
• wherein the first optical member, the scanning mirror and the second optical member are supported by the housing,
• wherein a space containing the scanning device is sealed by the first optical member, the second optical member and the housing,
• wherein the second optical member includes a first optical surface, a second optical surface, a third optical surface, a fourth optical surface, and a fifth optical surface,
• wherein the beam reflected by the scanning mirror is refracted by the first optical surface, then reflected by the second optical surface, then refracted by the third optical surface to direct to a reflecting and diffusing plate, then reflected and diffused by the reflecting and diffusing plate, then refracted again by the third optical surface, then reflected by the fourth optical surface, then reflected by the fifth optical surface, and then transmitted through the fourth optical surface to be directed to the emergence window, and
• wherein the image forming apparatus swings the scanning mirror, thereby forming an image on the surface to be scanned.