A plurality of ground-tint patterns are prepared. A ground-tint pattern adding unit adds a ground-tint data to a printing data to be output to a printer. The ground-tint data includes a copy-suppression pattern that is prepared by combining optically readable copy-surviving patterns with optically difficult-to-read copy-extinctive pattern and are manifested in reproductions. The ground-tint pattern adding unit changes the copy-suppression pattern in the ground-tint data to be added to the printing data with time.