Patent ID: 7755655

Claim:
An exposure device for exposing the charged surface of a photoconductive drum, comprising: a light source configured to emit light based on image information; a rotary multifaceted mirror configured to reflect the light emitted from the light source to scan the surface of the photoconductive drum; a driving mechanism configured to drivingly rotate the rotary multifaceted mirror; an inner casing configured to cover at least the driving mechanism and the rotary multifaceted mirror; an outer casing configured to cover the inner casing from the outside: an air vent configured to communicate the inside and outside of the inner casing being formed in a part of the inner casing facing the rotary multifaceted mirror; and a heat radiating plate configured to release heat generated inside the inner casing to outside, the heat radiating plate having a part extending outward from the outer casing, wherein the outer casing includes a bottom portion, an outer surrounding wall standing on the bottom portion, and an outer cover covering an upper opening of the outer surrounding wall, and at least the outer cover being free of openings therethrough, the inner casing includes an inner surrounding wall standing on the bottom portion inside the outer surrounding wall, and an inner cover covering an upper opening of the inner surrounding wall, and the outer cover is provided above the inner cover with a space therebetween, the air vent is provided at a position facing the rotary multifaceted mirror in the inner cover so that rotation of the rotary multifaceted mirror by the driving mechanism generates an air flow for diffusing air into the space between the outer cover and the inner cover, wherein the outer surrounding wall includes an upwardly projecting wall extending up from the bottom portion of the outer casing and a downwardly projecting wall projecting down from the outer cover of the outer casing, the upwardly projecting wall and the downwardly projecting wall of the outer casing being telescoped together and being substantially free of air vent openings therethrough.