A color image forming apparatus comprising: image forming means (22, 23, 24, 25, 26) adapted to form a plurality of mixed color patches and a monochromatic patch, the plurality of mixed color patches being formed by plural combinations with gradation values of each of colors of color materials including cyan, magenta and yellow and the monochromatic patch being formed by black; fixing means adapted to fix the plurality of mixed color patches and the monochromatic patch on a sheet; detection means adapted to detect the plurality of the mixed color patches and the monochromatic patch fixed on the sheet before the sheet is discharged, the detection means being positioned to be capable of detecting the plurality of mixed color patches and the monochromatic patch on the sheet before the sheet is discharged, and output color values based on the detection; correction means, based on the output color values of the plurality of mixed color patches and the output color value of the monochromatic patch detected by said detecting means, adapted to obtain combinations of gradations of each of the colors of the color materials whose color values are close to the output color value of the monochromatic patch to correct an image forming condition, wherein the plurality of mixed color patches is formed by the color materials including cyan whose gradation is increased and decreased, respectively, by a predetermined amount of gradation from a reference gradation in cyan for forming the plurality of the mixed color patches, magenta whose gradation is increased and decreased, respectively, by a predetermined amount of gradation from a reference gradation in magenta for forming the plurality of the mixed color patches, and yellow whose gradation is increased and decreased, respectively, by a predetermined amount of gradation from a reference gradation in yellow for forming the plurality of the mixed color patches. image forming means (22, 23, 24, 25, 26) adapted to form a plurality of mixed color patches and a monochromatic patch, the plurality of mixed color patches being formed by plural combinations with gradation values of each of colors of color materials including cyan, magenta and yellow and the monochromatic patch being formed by black; fixing means adapted to fix the plurality of mixed color patches and the monochromatic patch on a sheet; detection means adapted to detect the plurality of the mixed color patches and the monochromatic patch fixed on the sheet before the sheet is discharged, the detection means being positioned to be capable of detecting the plurality of mixed color patches and the monochromatic patch on the sheet before the sheet is discharged, and output color values based on the detection; correction means, based on the output color values of the plurality of mixed color patches and the output color value of the monochromatic patch detected by said detecting means, adapted to obtain combinations of gradations of each of the colors of the color materials whose color values are close to the output color value of the monochromatic patch to correct an image forming condition, wherein the plurality of mixed color patches is formed by the color materials including cyan whose gradation is increased and decreased, respectively, by a predetermined amount of gradation from a reference gradation in cyan for forming the plurality of the mixed color patches, magenta whose gradation is increased and decreased, respectively, by a predetermined amount of gradation from a reference gradation in magenta for forming the plurality of the mixed color patches, and yellow whose gradation is increased and decreased, respectively, by a predetermined amount of gradation from a reference gradation in yellow for forming the plurality of the mixed color patches.