An image forming apparatus is disclosed. The image forming apparatus includes an image bearing member, a developing device, a gap retaining member and a control unit. The control unit decreases a potential difference according to an increase in the drive amounts of the image bearing member and the developer bearing member. The decrease is based on a difference according to an increase in at least one of the drive amounts of the image bearing member and the developer bearing member. The control unit is also configured to determine whether to execute a mode based on information about at least one of the driving amounts of the image bearing member and the developer bearing member from when the developing device is initially installed or the developing device is replaced.