An image forming apparatus includes an image bearing member and an image formation unit for forming an image on the image bearing member. The image formation unit is provided with a charger for charging the image bearing member. A potential detector detects a surface potential on the image bearing member charged by the charger. A controller controls an image formation condition of the image formation unit on the basis of a potential detected by the potential detector. The controller controls the image formation condition on the basis of a plurality of detected potentials corresponding to respectively different non-image areas between sequentially formed images.