Disclosed is an image forming method to perform a printing for a plurality of sheets of paper, comprising: expressing any one region in a first color, the one region being one of a predetermined number of regions which are provided at an end part of each sheet of the plurality of sheets of paper and are continuous in an extending direction of the end part of the sheets; expressing the other regions except the one region in a second color; and printing an additional image in which the one region expressed in the first color is shifted sequentially in the extending direction of the end part of the sheets, in an order of the printing of each sheet of paper.