A data processing apparatus processing X-ray detection data from an object being inspected, outputted by an X-ray apparatus, with which beam-shaped X-rays having a preset continuous X-ray spectrum are radiated from an X-ray generator to the-object, the X-rays transmitted through the object are detected by a photon counting detecting unit to i) measure a count indicative of the photons of the X-rays received at each of a plurality of pixels of the detecting unit and in each of previously one or more energy bins(Bin 1 to Bin 3) set in the continuous X-ray spectrum, and ii) output the count as the X-ray detection data, wherein the data processing apparatus comprises: characteristic acquiring means (12) for acquiring X-ray attenuation amounts μt of a substance based on the outputted count at each of the pixels and in each of the X-ray energy bins, the X-ray attenuation amounts μt being defined by known thicknesses t of the object in a transmission direction of X-ray fluxes of the X-rays and linear attenuation coefficients μ of the object when the object is the same in type as the substance or is the substance composed of materials of which effective atomic number is substantially the same as an atomic number of the object; and correcting data calculating means (12) for calculating, i) for each of the X-ray energy bins and ii) at each of the pixels or each of pixel areas each being formed by two or more pixels, correcting data correcting the X-ray attenuation amounts μt acquired by the characteristic acquiring means, the correcting data being based on a linear target characteristic passing an origin of a two-dimensional coordinate system, the coordinate system having two dimensions assigned to both the thicknesses t and to the X-ray attenuation amounts μt, the linear target characteristic being set based on an X-ray energy amount corresponding to a representative monochromatic X-rays applied in calculation to each of the X-ray energy bins; characterized in that the data processing apparatus further comprises approximating means (S3) for approximating, based on a function of the thicknesses t, the X-ray attenuation amounts acquired by the characteristic acquiring means, and correction-coefficient calculating means (S3) for calculating, as the correcting data, correction coefficients for replacing the X-ray attenuation amounts μt approximated with the function, with the linear target characteristic of the X-ray attenuation amounts μt corresponding to monochromatic X-rays having an X-ray energy representing each of the X-ray energy bins; and the approximating means is configured to approximate the X-ray attenuation amounts μt with the function of the thicknesses t in each of a plurality of sections provided by dividing the thicknesses t, and the correction-coefficient calculating means is configured to calculate the correction coefficients in each of the sections. correcting data calculating means (12) for calculating, i) for each of the X-ray energy bins and ii) at each of the pixels or each of pixel areas each being formed by two or more pixels, correcting data correcting the X-ray attenuation amounts μt acquired by the characteristic acquiring means, the correcting data being based on a linear target characteristic passing an origin of a two-dimensional coordinate system, the coordinate system having two dimensions assigned to both the thicknesses t and to the X-ray attenuation amounts μt, the linear target characteristic being set based on an X-ray energy amount corresponding to a representative monochromatic X-rays applied in calculation to each of the X-ray energy bins; characterized in that the data processing apparatus further comprises approximating means (S3) for approximating, based on a function of the thicknesses t, the X-ray attenuation amounts acquired by the characteristic acquiring means, and correction-coefficient calculating means (S3) for calculating, as the correcting data, correction coefficients for replacing the X-ray attenuation amounts μt approximated with the function, with the linear target characteristic of the X-ray attenuation amounts μt corresponding to monochromatic X-rays having an X-ray energy representing each of the X-ray energy bins; and the approximating means is configured to approximate the X-ray attenuation amounts μt with the function of the thicknesses t in each of a plurality of sections provided by dividing the thicknesses t, and the correction-coefficient calculating means is configured to calculate the correction coefficients in each of the sections.