1. An image adjusting method for adjusting the image forming position of each color component image so that a plurality of color component images are superposed, comprising: a first step of forming a reference image of one color component; a second step of forming an adjustment image of other color component on the reference image in accordance with an adjusting value for a predetermined image forming position; a third step of detecting a superposed state of the reference image and the adjustment image thus formed; a fourth step of repeating the process of said first to third steps while changing the adjusting value sequentially within a predetermined range; a fifth step of acquiring a first candidate for the adjusting value for the image forming position where the two images are superposed, based on the result of detection in said third step; a sixth step of acquiring a second candidate for the adjusting value for the image forming position where the two images are superposed, after executing the process of said first to fourth steps using a reference image and an adjustment image different from the reference image and the adjustment image, respectively; and a seventh step of acquiring an adjusting value for the image forming position of the adjustment image based on the first and second candidates thus acquired.