PURPOSE: To eliminate the need of an image data expansion and contraction calculating processes in the main body of a document preparing device by reading image data from a picture input device with the arbitrary optimum resolution in accordance with the resolution of the printing device used for printing the image data.

CONSTITUTION: By providing an external storage device 14 which has a function for storing the dot resolution of a connectible printing device 2 before inputting image data from a picture input device 3 and stores the image data corresponding to designated plural or single dot resolution, adaptive image data are printed by discriminating the dot density of the printing device connected at the printing time, directly reading the image data having the discriminated dot density from the device 3, adding the printing-time dot resolution corresponding to the image data, and discriminating the dot resolution of the printing device at the printing time.