To improve the efficiency of number designated printing by selecting whether a bit map data or page data before developing is unloaded or not in response to the capacity of a memory to unload the conversion print information necessary for additional printing in the case of additionally printing the number of necessary additional pages after the part of all the pages are continuously printed.

When a host interface 2 receives print data from a host machine 15, a CPU 9 converts print data into converted print data (page buffer), outputs the developed bit map into a printer engine 14 to print it. At the time of delivering the sheet after printing, the page buffer or bit map of corresponding print processing page as conversion print information and print control information for print management is unloaded in an HDD 16 of the state before outputting to the engine 14. At this time, if the capacity of the HDD 16 is small, the page buffer having small data quantity is unloaded, and if the capacity is sufficient, the bit map which requires no unnecessary development is saved.