Patent ID: 8081363

Claim:
An optical beam scanning apparatus comprising: a light source configured to emit one or plural light fluxes; a pre-deflection optical system configured to give a predetermined characteristic to the light flux emitted from the light source; an optical beam deflecting device configured to deflect the light flux, which is given with the predetermined characteristic by the pre-deflection optical system, to a scanned object in a main scanning direction; a sensor configured to detect a portion of the light flux deflected by the optical beam deflecting device; and a post-deflection optical system including an imaging lens for imaging the light flux, which is deflected by the optical beam deflecting device, on the scanned object, the imaging lens having: a lens-shaped portion for imaging the light flux, which is deflected by a deflecting surface of the optical beam deflecting device and passed through an incidence surface of the imaging lens, onto a scanned surface of the scanned object, a totally reflecting surface-shaped portion having at least two totally reflecting surfaces for totally reflecting a part of the light flux, which is deflected from the deflecting surface of the optical beam deflecting device and passed through the incident surface of the imaging lens, the part of the light flux being totally reflected at least two times on the totally reflecting surfaces, and a transmission surface-shaped portion that has a transmission surface through which the part of the light flux, which is totally reflected by the totally reflecting surfaces, is transmitted, the part of the light flux transmitted through the transmission surface being directed to the sensor.