PURPOSE: To align the image data of the first proof and the second proof in a proof inspecting device for inspecting the different part between the first proof and the second proof.

CONSTITUTION: By this method for aligning the image data, the image data of the first proof and the second proof are displayed on a monitor, and the reference points of the respective image data are designated by two points (As, Ae) and (Bs, Be). A host computer arithmetically calculates an angle θand a moving amount (Xof, Yof) by which either image data is rotated in order to align the respective reference points. Either image data is coordinate- transformed, based on the angle θ and the moving amount (Xof, Yof) obtained. Thus, two image data are easily aligned.