1. A calibration data creating device comprising: a reference measured density memory storing, as reference measured densities, measured densities of reference density patches that are formed by an image-forming unit based on a reference density patch data for a plurality of reference set densities, the reference density patch data being binarized image data; a target density memory storing target densities in association with a plurality of set densities; a dither data memory storing dither data that has a plurality of dot locations and that is used for creating binarized image data based on each set density, the dither data having a prescribed threshold at each dot location; a corresponding set density determining unit determining corresponding set densities for the plurality of the reference set densities, the corresponding set density for each reference set density allowing the dither data to create binarized image data that enables the image-forming unit to form an image whose density corresponds to the measured density of the reference density patch that is formed by the image-forming unit based on the reference density patch data at the each reference set density; a calibration data creating unit creating calibration data indicating a correlation between the set densities and calibrated set densities, the calibrated set density for each set density allowing the dither data to create binarized image data that enables the image-forming unit to form an image whose density is the same as the target density for the each set density, the calibration data creating unit creating the calibration data based on the target densities, the reference measured densities, and the corresponding set densities; and a calibration data memory storing the calibration data.