An image forming apparatus comprising: a tone correction unit configured to convert image signal based on tone correction data representing a relationship between an input density of the image signal and an output density of the image signal; an image forming unit (1, 2, 3, 4, 6) configured to form an image on a printing material based on the converted image signal; a holding unit configured to hold the tone correction data; a reading unit configured to read a density of the image formed on the printing material; and an updating unit configured to update the tone correction data held in the holding unit, characterized in that the updating unit is further configured to: control the tone correction unit to convert patch image data including image signals for forming patch images, based on modified tone correction data; control the image forming unit (1, 2, 3, 4, 6) to form the patch images based on the converted patch image data, the patch images including a first patch image and a second patch image; control the reading unit to read densities of the patch images; and update the tone correction data based on the densities of the patch images, and the modified tone correction data are generated from the tone correction data, which are previously updated by the updating unit and held in the holding unit, such that an input density of an image signal corresponding to the first patch image is converted to a predetermined output density corresponding to a target maximum density. a tone correction unit configured to convert image signal based on tone correction data representing a relationship between an input density of the image signal and an output density of the image signal; an image forming unit (1, 2, 3, 4, 6) configured to form an image on a printing material based on the converted image signal; a holding unit configured to hold the tone correction data; a reading unit configured to read a density of the image formed on the printing material; and an updating unit configured to update the tone correction data held in the holding unit, characterized in that the updating unit is further configured to: control the tone correction unit to convert patch image data including image signals for forming patch images, based on modified tone correction data; control the image forming unit (1, 2, 3, 4, 6) to form the patch images based on the converted patch image data, the patch images including a first patch image and a second patch image; control the reading unit to read densities of the patch images; and update the tone correction data based on the densities of the patch images, and the modified tone correction data are generated from the tone correction data, which are previously updated by the updating unit and held in the holding unit, such that an input density of an image signal corresponding to the first patch image is converted to a predetermined output density corresponding to a target maximum density. control the tone correction unit to convert patch image data including image signals for forming patch images, based on modified tone correction data; control the image forming unit (1, 2, 3, 4, 6) to form the patch images based on the converted patch image data, the patch images including a first patch image and a second patch image; control the reading unit to read densities of the patch images; and update the tone correction data based on the densities of the patch images, and the modified tone correction data are generated from the tone correction data, which are previously updated by the updating unit and held in the holding unit, such that an input density of an image signal corresponding to the first patch image is converted to a predetermined output density corresponding to a target maximum density.