An image forming apparatus is capable of executing an auto paper selection function for automatically selecting a paper size corresponding to a paper size of an input document from a plurality of paper cassettes, and an auto magnification selection function for automatically magnifying an image of the input document to correspond to a defined paper size. The auto magnification selection function is selected for execution by the apparatus when there is only one size of paper to be selected in the apparatus, and the auto paper selection function is selected for execution by the apparatus when there are a plurality of sizes of paper to be selected in the apparatus.