The present invention aims to provide an image forming apparatus and the like that perform a highly-accurate tone correction in a relatively short time and includes the following: a pattern former, with use of each image forming unit, on a sheet, forming tone patches in the main or sub scanning direction (41k,c,y,m) and aligning markers, which indicate positions of the tone patches, in the same direction as the tone patches (42k,c,y,m); a pattern reader reading the sheet with the tone patches and markers formed thereon; a coordinate determiner determining coordinates of the tone patches in the direction of the aligned tone patches based on the read markers (42k,c,y,m); a density determiner determining densities of the tone patches (41k,c,y,m) read based on the determined coordinates; and an updating part updating the tone correction table based on relationships between the determined densities and tone levels.