In the case of performing duplex printing on a continuous sheet, by setting a length of a non-image area to an optimum length, both of mark detection having high reliability and the suppression of a sheet consumption amount are achieved. For this purpose, when duplex printing of a plurality of images on front and back surfaces of the continuous sheet is performed, on the basis of a length of the image to be printed precedently to a non-image area W3 on the second surface, the length of the non-image area common to the front and back surface is set.