An image forming apparatus including an image bearing member, a charging unit for charging the image bearing member, and an image exposure unit including a light emitting portion for emitting light to form an electrostatic image. The image forming apparatus also includes a developing unit including a toner carrying member and a bias controlling unit for applying a bias voltage to the toner carrying member, the developing unit being effective to develop the electrostatic image with toner by a potential difference between the toner carrying member and the electrostatic image, a potential difference determining unit, and a storing unit for storing a light amount control value, corresponding to the potential difference, set on a basis of a light emission amount information inherent to the light emitting portion. The image exposure unit reads the light amount control value and controls the light amount based on the light amount control value.