an image forming apparatus including a rotatable photosensitive member , charging means for charging the photosensitive member at a predetermined potential , developing means for supplying toner to the photosensitive member to provide a developed image , transfer means including a transfer roller for transferring the developed image to a paper sheet , paper removal detecting means for detecting that a jammed paper is removed from the image forming apparatus , stopping means responsive to the jammed paper removal detecting means for stopping supply of the toner to the photosensitive member , rotating means responsive to the paper removal detecting means for rotating the photosensitive member and the transfer roller , and setting means responsive to the paper removal detecting means for setting the circumference of the transfer roller alternately in a first state , in which the circumference of the transfer roller is supplied with a first voltage more negative than the predetermined potential of the photosensitive member , and in a second state in which the circumference of the transfer roller is supplied with a second voltage more positive than the predetermined potential of the photosensitive member .