An image forming apparatus includes a creating portion for determining whether or not document data give have a capacity greater than a first predetermined value, and creating code patterns by encoding the document data as it is, if the controller determines that the document data have a capacity smaller than the first predetermined value, a creating portion for reducing the document data by a second predetermined value and creating code patterns by encoding the thus reduced document data, if the controller determines that the document data have a capacity greater than the first predetermined value, and an printing engine for forming the thus created code patterns and the document data on a sheet of paper. With this arrangement, it is possible to print even large-capacity document data on the back of the sheet of paper in the form of code patterns.