1. An image forming device comprising: an input unit for input of dot information specifying a desired size of dots in an image; a memory unit storing a test pattern and information relating a reference density and a parameter controlling a density of the image to a size of dots in an image of the test pattern, the information being obtained by measuring a density and size of dots in the image of the test pattern; an image forming unit for forming the image of the test pattern stored in the memory unit according to the parameter related to the size of dots corresponding to the desired size of dots specified by the dot information input by the input unit; a density detector for detecting a density of the image formed by the image forming unit; and a processing unit for obtaining the reference density related to the size of dots corresponding to the desired size of dots specified by the dot information input by the input unit from the information stored in the memory unit, performing a comparison of the reference density with the density detected by the density detector, and adjusting the parameter according to a result of the comparison, and adjusting the density of the image by applying the adjusted parameter.