An image forming apparatus includes a controller for performing a mode, in which an image portion potential is controlled during image formation so that an absolute value of the image portion potential is a first value when a resistance value of a developing roller based on a value of a current flowing between the developing roller and an electroconductive member is smaller than a predetermined value when a predetermined potential difference between the developing roller and the electroconductive member is formed during non-image formation and so that an absolute value of the image portion potential is a second value smaller than the first value when a resistance value of the developing roller based on a value of current flowing between the developing roller and the electroconductive member is not smaller than the predetermined value when the predetermined potential difference between the developing roller and the electroconductive member is formed during non-image formation.