An image-forming device includes: an image-forming unit; a sensor; a storing unit; a reference ratio determining unit; an estimated ratio determining unit; and a density correcting unit. The image-forming unit is capable of forming a plurality of density patches corresponding to a plurality of reference densities. The sensor detects the densities of the density patches and outputs a measured output value for each reference density. The storing unit stores reference output values for the reference densities. The reference ratio determining unit determines reference ratios to compensate for differences between the measured output values and the reference output values for the reference densities. The estimated ratio determining unit determines estimated ratios corresponding to densities other than the reference densities based on the reference ratios for the reference densities. The density correcting unit corrects density of image data based on the reference ratios and estimated ratios.