An image forming apparatus including, an image bearing member, an image forming device for forming a toner image on the image bearing member, a transfer device for electrostatically transferring the toner image formed by the image forming device on the image bearing member to a transfer material, an detector for detecting temperature and humidity in a main body of the apparatus and a controller for such control that the toner amount per unit area of the toner image formed on the image bearing member by the image forming device differs in accordance with a result detected by the detector.