The type and/or properties of a substance is identified highly accurately regardless of the thickness of the substance. A data processing apparatus (12) processes counts detected at each of pixels of a photo counting detector (26) in each of a plurality of energy ranges of X-rays, the X-rays being radiated from an X-ray tube, (21) transmitted through an object. The apparatus (12) includes means (35) calculating an image of the object (OB) based on the counts, and means (35) setting a region of interest on the image. The apparatus (12) further includes means (35) removing, from the pixel, pixel information showing a background present in the region of interest, and means (35) calculating, pixel by pixel, inherent information inherent to the substance, based on the counts detected at each of the respective pixels in each of the energy ranges of the X-rays in the region of interest, the inherent information indicating a transmission characteristic inherent to the X-rays.