an image forming apparatus includes a rotatable image bearing member and a toner image former for forming a toner image on the image bearing member , wherein the toner image former is capable of forming a toner image having a predetermined width measured in a direction of a rotational axis of the image bearing member at each of different positions , a transfer member , pressed against the image bearing member , for forming a transfer portion for transferring the toner image onto the transfer material from the image bearing member , a current detector for detecting a current flowing through the transfer member , a calculating portion for calculating a resistance difference in the transfer member with respect to the axial direction , on the basis of outputs of the current detector , for the toner images at the different positions when the toner images pass through the transfer portion , and an output portion for outputting an abnormality on the basis of an output of the calculating portion .