An image forming apparatus includes: a storing section, an image forming section to form a measurement image to output a measurement chart, and a control section for inputting density information indicating densities at positions of the measurement image, to calculate a correction value corresponding to each position based on the density information, to store the value in association with an output condition including a screen condition indicating a screen processing at the time of outputting the chart, to determine the output condition of the image data, to read the value corresponding to the output condition, and to correct the image data based on the value, wherein the image forming section forms an image based on the corrected image data, and when no correction value corresponding to the screen condition of the input image data is stored in the storing section, the control section inhibits the correction from being executed.