Patent ID: 7218337

Claim:
An optical scanner which irradiates a light beam to a scanned surface of an image support to form an electrostatic latent image on the image support surface, comprising: a light source emitting a light beam; at least one final-stage reflection mirror having a reflection surface which reflects a reflected light beam from a polygon mirror directly to the scanned surface of the image support, a first axis parallel to a main-scanning correspondence direction on the reflection surface, and a second axis along the reflection surface and perpendicular to the first axis; an optical element adjusting a position of a scanning line in a sub-scanning correspondence direction, the optical element having a beam-incidence surface, a third axis parallel to the main-scanning correspondence direction on the beam-incidence surface, and a fourth axis perpendicular to the third axis and along a beam-incidence direction; a first adjustment unit provided to rotate said at least one final-stage reflection mirror around the second axis in order to attain uniformity of a scanning speed of the optical scanner in the main scanning direction; a second adjustment unit provided to rotate said optical element around the fourth axis in order to correct an inclination of the scanning line in the sub-scanning correspondence direction to a desired position of the scanning line, at least one of the first adjustment unit and the second adjustment unit being provided with an electrically driven actuator; a detection unit detecting an error of the scanning speed of the optical scanner; and a control unit controlling driving of the actuator based on the scanning speed error detected by the detection unit, wherein said at least one final-stage reflection mirror is a half mirror, and the detection unit detects the error of the scanning speed based on a difference of detection times of the light beam detected by a plurality of photodetectors, said plurality of photodetectors being arranged on a back surface of the half mirror apart from one another at a given interval.