An image forming apparatus includes: a specification unit configured to perform surface specification processing for specifying a reflective surface that deflects light; a correction unit configured to perform correction processing for correcting image data in accordance with which reflective surface deflects light; and a control unit configured to control so as to cause scanning of a first photosensitive member to start before the surface specification processing completes, and control so as to, after the surface specification processing completes, cause the correction processing to be performed, with respect to image data for causing light to be emitted from a second light source and in accordance with a specification result of the surface specification processing, and cause scanning of the second photosensitive member to start.