A first imaging unit obtains a first radiation image, which is imaged under first imaging conditions. A second imaging unit obtains a plurality of projection images by tomosynthesis imaging under second imaging conditions. A reconstructing unit reconstructs a plurality of projection images to generate a plurality of tomographic images of cross sectional planes of a subject. An image synthesizing unit generates a second radiation image employing the plurality of tomographic images. A subtraction processing unit administers a subtraction process on the first and second radiation images, to generate a subtraction image.