1. A density detection apparatus comprising: a storage unit that stores therein image information concerning a plurality of density detection images having different area ratios and being linearly arranged in a predetermined order; a measuring unit that measures amounts of light components reflected by an image carrier or by the plurality of density detection images formed on the image carrier; a light amount obtaining unit that obtains a variation in amounts of light components reflected by each of a plurality of regions in which the plurality of associated density detection images are formed, on the basis of values of the measured amounts of light components reflected by the image carrier, and that obtains, as a reference value, a representative value of the amounts of light components reflected by each of the plurality of regions; an image correcting unit that corrects the image information stored in the storage unit by changing an arrangement order of the plurality of density detection images so that density detection images having area ratios which are equal to or smaller than a first threshold are to be formed in regions having variations in the amounts of light components which are equal to or smaller than a second threshold; an image forming unit that forms the plurality of density detection images on the image carrier on the basis of the corrected image information; and a density obtaining unit that obtains image density levels for the plurality of density detection images corresponding to the area ratios of the plurality of density detection images by using the amounts of light components reflected by the plurality of density detection images and the reference values set for the plurality of regions in which the plurality of associated density detection images are formed.