An image forming apparatus in which the intensity of a light beam used to form a latent image is switched in response to a change in resolution. A laser (101∼104) emits a light beam for forming a latent image on a photosensitive drum (203). A polygon mirror (105) scans the emitted light beam. BD sensors (106,107) detect the scanned beam. A timing controller (204) selects the preferable timing from a storage device table (205) according to the intensity of the light beam or the resolution when controlling the light emission timing of the lasers in response to a detection of timing of the detected light beam.