an image former that forms a plurality of adjustment images on a sheet, the plurality of adjustment images being for aligning a printing image by adjusting a forming position of the printing image according to distances between ends of the sheet and positions of the plurality of adjustment images, wherein the plurality of adjustment images are formed at positions that are asymmetrical with respect to a center of the sheet;

a detector disposed to stride over one end of a pair of ends and not to stride over another end of the pair of the ends, the pair of the ends being along a conveyance direction of the sheet, the detector configured to detect a position of the one end and a plurality of adjustment image positions, one for each of the plurality of adjustment images formed in a direction orthogonal to the conveyance direction on the sheet; and

a control section configured to calculate each distance from the position of the one end to each of the plurality of adjustment image positions,

wherein the image former adjusts the forming position of the printing image based on the calculated distances.