In the image forming apparatus, when the document data is developed to generate the print data in order to print out by the document data, the possibility of repeated requests to print out by the document data is determined by whether or not the document data is stored in the shared directory, or whether or not the document data is attached to the electronic mail distributed to a plurality of people. If the need of storing the document data has been determined, the document data is stored in the image forming apparatus. Upon receipt of a request to print out by the same document data as this document data, the stored print data is used for printing.