An image forming apparatus, including a photosensitive member, a scanning optical unit configured to scan the photosensitive member by laser light according to image information, a detection unit arranged in a position facing the photosensitive member and configured to output positional information on the laser light. The detection unit includes a detection portion into which the laser light reflected by the photosensitive member is incident, and a control unit configured to calculate a positional deviation amount of an irradiation position on the photosensitive member which is irradiated by the laser light based on the positional information output by the detection unit, and control the scanning optical unit to correct the positional deviation of the irradiation position of the laser light.