1. An image processing apparatus comprising: image input means for reading a document image; area specifying means for specifying an arbitrary area in the document image read by said image input means; interval specifying means for specifying arbitrary intervals in the document image; dimension calculating means for calculating a dimension of the intervals; dimension input means for inputting a prescribed dimension of the intervals; ratio calculating means for calculating a ratio of the calculated dimension to the prescribed dimension; first magnification setting means for setting a reciprocal of the ratio as a first magnification of the specified area which has been specified by said area specifying means; first conversion means for converting a size of a first image within the specified area in accordance with the first magnification; second magnification setting means for setting a second magnification of an unspecified area so that a second image in the unspecified area does not exceed a predetermined size of sheets, the unspecified area being other than the specified area on a sheet of a predetermined size which is provided for the first image whose size has been converted by said first conversion means; second conversion means for converting the size of the second image in accordance with the second magnification; and combining means for combining image data of both the images whose sizes have been converted by said first and said second conversion means.