1. An image-forming device, comprising: an image-forming unit forming an image on a recording medium based on inputted image data; a test image memory storing a plurality of sets of test image data, each set of test image data corresponding to one of a plurality of test images, each set of test image being used for calibrating density of image to be formed by the image-forming unit; a test image forming unit controlling the image-forming unit to form the plurality of test images based on the plurality of sets of test image data a density measuring unit measuring the density of each test image that the image-forming unit has formed on the recording medium; an abnormality determining unit comparing the density of each test image measured by the density measuring unit with prescribed values that are pre-stored in association with the corresponding set of test image data to determine whether the measured density of the test image is abnormal, a set of test image data that corresponds to a test image whose measured density is determined to be abnormal being a set of to-be-reformed test image data; and a test image re-forming unit that, if there is at least one set of to-be-reformed test image data in the plurality of sets of test image data, controls the image-forming unit to re-form a test image based on the at least one set of to-be-reformed test image data, the test image re-forming unit controlling the image forming unit not to re-form a test image based on those test image data that is other than the at least one set of to-be-reformed test image data, the test image reforming unit controlling the measuring unit to measure the density of the reformed test image.