A method of controlling printing is provided, by which poster printing and double-sided printing are realized at the same time by suitably controlling an order of outputting pages for a divided image. A printer 1500 capable of double-sided printing prints two consecutive pages of print data on both sides of a sheet of paper, and a host computer 3000 generates print data such that each of the pages of print data is enlarged and divided and resultant data is printed on a plurality of media. Therefore, a first page of print data is divided into a predetermined number of pieces of print data in accordance with the number of sheets of print paper, and a second page of print data is also divided in the same manner. Next, a particular piece of print data for the first page and a particular piece of print data for the second page are selected from the predetermined number of pieces of print data for each of the first and second pages. Then, the selected pieces of print data for the first and second pages are output to the printer 1500 so that they are printed on a front and back sides, respectively, of a medium.