To enable a binding processing by matching the size of image data by performing a variable power processing to the stored image data so that the image data stored in an image storage means becomes the same size as a calculated image area when the image data stored in the image storage means is different from the image area calculated by an image area calculating means.

Once size specification of a recording sheet has been confirmed as, e.g. A3, by the binding processing of a page description language from a binding instruction command, A4 as a half size of the recording sheet is judged to be an optimal size for image arrangement, the image data of the A4 size is generated and a formatter part 8 is informed to transmit the image data to image memory 9 by a core part 10. Reduced variable power is instructed to the core part so that the image data becomes the A4 size when the developed image data is larger than the A4 size after the page description language is developed to the image data and the image data after the reduced variable power is transmitted to the image memory 9 by the informed formatter 8.