A data converter 14 converts a spooled print control code into a display data of a predetermined structure. The converted data is displayed on a displaying device. The user checks the displayed data. When the data is to be edited, the user designates the region to be edited and inputs contents of the change. In accordance with the change contents, a data edit controller 15 changes the display data. A data inverse converter 16 converts the changed display data into the structure of the original print control code, and restores the converted data into a spool file 13. The print control code which is restored is read out by a despooler 17, and then transferred to a printing device through transfer controlling means.