A host device successively sends print data constituting a plurality of sets of copies of a document to be printed to a printer capable of printing on both sides of printing paper. If each set of copies to be printed consists of an odd number of pages, a blank page is inserted as the reverse side of the last page to make the total number of pages of the set of copies an even number. The print data thus created is sent to the printer as a single job. This makes it possible to prevent the last page of one set of copies and the first page of another set of copies from being printed on the same sheet of paper, thereby allowing each set of copies to be printed as a discrete set independent of other sets. Print job management is performed on the basis of a single print job.