1. An image forming apparatus comprising: print data generating unit for generating gradation correction test chart print data to juxtapose and draw a basis density pattern having a basis density of a yellow color of various colors including the yellow color used for multicolor printing and a plurality of reference density patterns having respective densities of the yellow color to be compared with the basis density and additionally draw a contrast effect pattern composed of colors having a contrast effect on the yellow color for the basis density pattern and the reference density patterns of the yellow color; printing unit for printing a gradation correction test chart including a yellow color gradation correction pattern in which the basis density pattern and the plurality of reference density patterns are juxtaposed and printed and the contrast effect pattern is additionally printed, based on the gradation correction test chart print data generated by the print data generating unit; receiving unit for receiving an input of a density adjustment value of any pattern based on a shading comparison of the basis density pattern and the reference density patterns by a user's visual observation of the density correction test chart printed by the printing unit; and gradation correcting unit for performing a gradation correction of any pattern based on the density adjustment value of any pattern received by the receiving unit.