A calibration data creating device includes a reference measured density memory, a dither data memory, a corresponding set density determining unit, a calibration data creating unit, and a calibration data creating unit. The reference measured density memory stores measured densities of reference density patches that are formed by an image-forming unit based on the reference density patch data. The dither data memory stores dither data that has a plurality of dot locations, the dither data having a prescribed threshold at each dot location. The corresponding set density determining unit determines corresponding set densities for the plurality of the reference set densities. The calibration data creating unit creates 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.