1. An image forming apparatus comprising: an image forming section configured to include a plurality of image forming units that individually form images of different colors, and perform image forming by superimposing images of two colors individually formed by two of the image forming units; a chart creation section configured to input, to the image forming section, image data of a chart that includes first lines serving as a plurality of lines containing a reference color serving as one color of the two colors, the plural lines being located in parallel at specific intervals, and a stepped image that has second lines serving as a plurality of lines containing an adjustment color serving as the other color of the two colors, the plural lines being parallel to the first lines and having equal line widths, wherein between the first lines, equal line width portions in the individual second lines are located with positions thereof shifted in order, so as to be headed from one of the first lines to the other in the stepped image; an input section configured to receive input of an adjustment value that is selected based on the chart formed by the image forming section; and a color shift correction section configured to move, in response to the adjustment value inputted to the input section, an image forming position of the image forming unit forming an image of the adjustment color with respect to an image forming position of the image forming unit forming an image of the reference color in the image forming section.