PURPOSE: To easily and accurately duplicate a printed page by checking such an error instruction that an approximation bit map is compared with source display, and using the image approximation.

CONSTITUTION: This device 10 converts the printed page 12 into a series of page definition language expressions or commands suited to one or more output devices 14. The device 10 is provided with a computer 16 constituted of a personal computer. Then, a set of set recognition parameters are used and the source display is converted into the image approximation expressed by the page definition language and further converted to the approximation bit map. The approximation bit map is compared with the source display of a bit map form and the error instruction is obtained. When the error instruction matches with a specified reference, the image approximation is used as page definition language display. When it does not, one or plural other image approximations expression by the page definition language are led, the error instruction are obtained, whether or not they respectively match with the specified reference is checked, and when they do, the image approximations are used.