Patent ID: 7898562

Claim:
An exposing device which radiates light on a photoconductor drum which rotates, thereby executing exposure, comprising: a light-emitting element unit including at least one light-emitting element having an emission area which emits light that is generated, the emission area having a rectangular shape with a long side along a direction perpendicular to a rotational direction of the photoconductor drum, and a short side along the rotational direction, the short side being shorter than the long side; a lens unit which focuses the light, which is emitted from the emission area of the light-emitting element, on a peripheral surface of the photoconductor drum, thereby executing exposure, and forming on the peripheral surface a beam spot having a shape corresponding to the shape of the emission area; and a driving circuit which drives the light-emitting element of the light-emitting element unit at a predetermined cycle time and causes the light-emitting element to emit light continuously for a light-emission period that is shorter than the cycle time, within the cycle time, thereby making a width of the beam spot formed on the peripheral surface within the cycle time, in a direction along the rotational direction, close to a width of the beam spot in the direction perpendicular to the rotational direction; wherein the light-emission period is set at T×(1−m), where m is a ratio of the short side to the long side of the emission area and T is the cycle time.