The utility model relates to an ally oneself with that roll web gathers leaves of a book that cutting machine uses cut automatic mechanism of correcting of size. The problem that will solve is exactly that the background art exists: current ally oneself with the roll web that allies oneself with that the roll web gathered leaves of a book on the cutting machine more and when cutting, owing to the change of scroll tension elasticity, cut the size throw off, influence the problem of finished product quality. The problem of this technique is solved the technical scheme main points that adopt are: set up the color code detection device that detects first line of a couplet paper color code position, the control system feedback driving servo motor of color code detection device, the last synchronous pulley of servo motor drives the synchronous pulley who cuts out on the cutter shaft and adjusts. Can be applied to and ally oneself with the roll web more and gather leaves of a book and cut.