In accordance with an embodiment, an optical scanning apparatus for exposing a photoconductor includes a light source, a deflecting device, an imaging optical system and a light-guiding optical system. The light source configured to emit a light beam. The deflecting device configured to deflect and scan the light beam from the light source. The imaging optical system configured to form an image by using the deflected and scanned light beam on the photoconductor. The light-guiding optical system configured to guide the light beam passing through the imaging optical system to a photodetector.