An image forming apparatus including an exposure device, a development device, an image density detection device, a supply device for supplying a toner to the development device, a cleaning device for cleaning the surface of an image bearing member, a driving torque detection device for detecting a driving torque of the image bearing member, and a controller which drives the image bearing member while providing a predetermined electric potential difference between a region charged in the image bearing member and a developer support in case of non-image formation conducts a driving torque detecting operation with respect to the image bearing member by means of the driving torque detection device, and changes a reference value in response to the value of the driving torque detected.