Patent ID: 7583282

Claim:
An image printing apparatus for printing images on front and back surfaces of a sheet, comprising: an image printing section which forms the image for the front surface of the sheet as well as an image of a reference mark on a photosensitive member at one portion in a region outside an image region and transfers the images formed on the photosensitive member onto the front surface of the sheet; a fixing unit which fixes the transferred images on the sheet; a sensor which detects the reference mark by scanning at least two scanning lines of the reference mark after fixing printed on the front surface of the sheet; an arithmetic operating section which obtains a shrinkage factor of the sheet on the basis of a size of one and only one reference mark before fixing and a size of the one and only one reference mark after fixing and calculates a position and magnification of the image to be printed on the back surface on the basis of the shrinkage factor; and a control section which performs control operation to print the image on the back surface of the sheet on the basis of the calculated position and the calculated magnification.