To print, by discriminating a second user, print data unprintable by first user's printing authority, a control method for an image forming apparatus, printing print data specified by user discrimination information, comprises: reading discrimination information; obtaining printing authority information corresponding to first user discrimination information for discriminating a first user specified by discrimination information of the first user; judging whether input print data can be printed based on the printing authority information corresponding to the obtained first user discrimination information; determining, if judged that the input print data is unprintable based on the printing authority information corresponding to the first user discrimination information, printable print data based on printing authority information corresponding to second user discrimination information for discriminating a second user specified by discrimination information of the second user; and printing the printable print data.