PURPOSE:To facilitate the expansion of print and form patterns or the like by inserting an image data into a form overlay data in a information processing system printer. CONSTITUTION:The image data for a code is loaded into a character generator 12 from an upper equipment 1, so that commonly used KANJI characters are stored in a usual manner. On the other hand, among characters or graphic to be used in a print data or a form overlay, those which are kept in each entry 15 of the character generator 12 are prepared as follows: they are brought in one unit into a pi-charactor registration buffer 5 as the pi-characters from an external file memory 2 in the upper equipment 1 and stored into each entry 16 of the pi-charactor registration buffer 13 containing a page printer 7 while a corresponding code is stored into a memory address 14. A form overlay data from the external file memory 2 is applied to a buffer 11 and a print data to a buffer 10 to start a printing. Thus, the expansion of a form pattern or the like can be done easily.