An image forming apparatus includes an image bearing member, an image forming unit for forming an image on the image bearing member and a detector for detecting the surface potential of the image bearing member, wherein a first image forming mode and a second image forming mode in which the image forming conditions of the image forming unit are different from each other can be selected, and further, the apparatus includes a controller for controlling the image forming conditions in the first and second image forming modes on the basis of the result detected by the detector for the first image forming mode.