To resolve a problem that, in the case that image data of front and rear faces of a double-sided document encoded with different encoding coefficients is laid out in a page aggregation (Nin1) format, re-compression on a memory is required for matching the encoding coefficients of the image data of the front and rear faces, which requires an excessive processing time for the re-compression, and which causes increase in cost of a device for the purpose of providing image processing means and the memory.

A compound machine simultaneously reading out front and rear faces of a double-sided document to make a copy by page aggregation, has an image formation device, in the case that at least one readout image data of front and rear faces could not be stored in a memory, performing re-reading by using the same coefficient resulting in higher compression than the previous reading as encoding coefficients for the front and rear faces.