pages to be printed is odd no extra page is printed but alternatively when the number of pages is odd extra one page may be printed as a blank sheet however it takes more time to print one page for the blank sheet also in the above examples the generation of the page position table is first made collectively in both side printing but alternatively it may be made in sequence during the printing of even page also in the above examples the end of page is detected by analyzing the print data during printing but alternatively the end of page may be judged as the top position of the next page by referring to the page position table also in the above examples a page printer was used but alternatively any other printers may be used also the end signal and the jam signal may be on the independent signal line or sent as the status data via a bi directional interface such as rs232c ieee or p1284 furthermore in the above examples the printing of next page is not started until the printing of one page is ended but the printing of next page may be started before the printing of one.