To perform exact calibration without being influenced by density between patches.

The image forming apparatus forming image data by the use of recording material of t colors (t is an arbitrary natural number) has a density correction part for correcting the density of the image data, which has a patch pattern for correcting the density of the image data, wherein the patch pattern has a patch column obtained by arranging m (m is an arbitrary natural number) patches having different density in the main scanning direction of the image forming apparatus in density order for every color of the recording material, and the patch columns are arranged by t rows so that the respective first patches may be at the same position up and down in the subscanning direction of the image forming apparatus, and constituted so that the densities of the n-th (all the natural numbers satisfying 1nm) patches arranged up and down in the patch column can be equal to each other, whereby the density of the image data is corrected on the basis of a colorimetric value obtained by performing the colorimetry of the patch pattern on a printing medium after outputting the patch pattern to the printing medium.