Image forming apparatus including corona charger

An image forming apparatus includes a photosensitive member; a corona charger provided with a discharging wire for electrically charging the photosensitive member; an exposure device for exposing to light the photosensitive member; a developing device for developing the electrostatic image; a transfer device for transferring the toner image onto a sheet; an adjusting device for adjusting a distance from the discharging wire to the photosensitive member; a detecting device for detecting information corresponding to a surface potential of the photosensitive member at least two points; and an executing device configured to execute an operation in a mode in which an image including a reference mark positioned at a reference portion of said corona charger, for adjusting the position of the discharging wire by the adjusting mechanism and an adjusting mark for adjusting a distance of the discharging wire from the photosensitive member.