An image forming apparatus includes an image forming section that forms a pattern image for detecting image-position displacement with respect to a lenticular lens sheet. The pattern image includes periodic images in each of which set images, each including two or more images of different shades and having a length equal to a lens pitch of the lenticular lens sheet, are arranged in a lens transverse direction of the lenticular lens sheet. The periodic images are arranged in a lens longitudinal direction of the lenticular lens sheet so as to be gradually shifted from one another in the lens transverse direction by a distance less than the lens pitch.