1. A radiation-image processing device that performs image processing including gradation processing on a radiation image acquired by irradiating a photographic subject with radiation, the radiation-image processing device comprising: determination unit for determining that a diagnosis target is a bone portion of the photographic subject; region extraction unit for extracting, as an anatomical region, a soft portion region corresponding to a soft portion of the photographic subject from the radiation image; feature amount calculation unit for calculating a feature amount of a density of the radiation image based on the soft portion region; and image processing unit for performing image processing including the gradation processing on the radiation image so that the feature amount becomes a target density.