An image forming apparatus that forms an output image corresponding to input image data on an image carrier by superimposing toner images of colors, includes a hardware processor that: detects color information of the output image for every pixel region; converts color information of the input image data for every pixel region and color information of the output image for every pixel region into indexes which define colors in predetermined color space coordinates; extracts a pixel region in which the color information of the output image is different from the color information of the input image data, and corrects the color information of the input image data with respect to the extracted pixel region; and stores the color information of the input image data as data for calibration in combination with the color information of the output image and image forming conditions when forming the output image.