1. An image forming apparatus comprising: recording means for recording an image on paper using a developer; reading means for reading an image of a given document; black ratio calculating means for calculating the black ratio of the image of said document on the basis of an output of said reading means; number-of-copies calculating means for calculating a number of copies which can be outputted corresponding to a defined capacity of the developer which is determined by the image forming apparatus on the basis of the black ratio calculated by said black ratio calculating means; and displaying means for displaying the number of copies which can be outputted which is calculated by said number-of-copies calculating means.