A density adjustment method for adjusting a density of a diagnostic image, having the steps of; exposing an image; developing the latent image; measuring a density of the developed image; creating a lookup table for relating the diagnostic image data and amount of exposure so as to form a density specified by the diagnostic image data; and correcting at least one of an exposure condition and a development condition to ensure that the next film has the optimized density, based on the difference between the measured density of a partial area of the film, and a density for comparison; wherein, a density of a prescribed area in a test exposure image is used as the density for comparison; while the exposure amount is used for exposing the partial area of the film at the time of forming a diagnostic image.