1. An image forming apparatus which forms an image in accordance with an electrophotographic method, comprising: storage means for storing image data; image processing means for performing image processing on the image data stored in said storage means; and image formation means for forming an image using developer based on the image data processed by said image processing means, wherein said image processing means includes developer consumption amount calculation means for generating information on a predicted amount of the developer consumed by said image formation means, based on the image data processed by said image processing means, and wherein said image formation means supplies the developer in correspondence with said information generated by said developer consumption amount calculation means.