An image forming apparatus includes image bearing member having a movable surface; charging means for charging the surface of the image bearing member; image exposure means for exposing the surface of the image bearing member charged by the charging means to light in accordance with image information, thus forming an electrostatic image; developing means for developing the electrostatic image formed on the image bearing member into a developed image; surface potential detecting means for detecting a potential of the surface of the image bearing member; discharging means for discharging the surface of the image bearing member; changing means for changing an image forming condition, wherein an area of the image bearing member passes the discharging means under different operating conditions of the discharging means, and the area is charged by the charging means, the changing means changes the image forming condition on the basis of a result of detection, by the surface potential detecting means, of surface potentials of the area charged by the charging means.