A system control unit causes a diagnosis monitor to display a plurality of sample images generated by changing one or more image processing parameters used in image processing of an X-ray image. When an operator designates a mixing ratio, at which the sample images are mixed, after the plurality of sample images are displayed on the diagnosis monitor, the system control unit sets one or more image processing parameters to be used when image processing of an X-ray image is performed based on the designated mixing ratio. An image processing unit performs image processing of an X-ray image input from an image input unit based on the set image processing parameter.