A data processing apparatus for inspecting an object based on amounts of X-rays transmitted through the object, X-ray detecting means that detects amounts of the X-rays transmitted through the object in each of n-number X-ray energy bins (n is a positive integer of 2 or more) which are set in advance to the X-rays, and outputs detection signals corresponding to the transmitted amounts; information acquiring means that acquires, based on the detection signals detected by X-rax detecting means, information showing a thickness t of the object and an average linear attenuation coefficient μ in a transmission direction of fluxes of the X-rays, in each of the energy bins; wherein the apparatus comprises: information acquiring means obtains imaginary attenuation values μ im (t) * t and calculated linear attenuation values μ io (t) * t corresponding to the monochromatic X-rays from the imaginary attenuation values μ im (t) * t by multiplying previously prepared correcting data C(t), and obtains information on a thickness t of the object and the average linear attenuation coefficients μ from the linear attenuations values μ io (t) * t, pixel data calculating means that calculates pixel data composed of pixel values each obtained by multiplying addition information by the thickness t, based on the information acquired by the information acquiring means, the addition information being obtained by mutual addition of the average linear attenuation coefficients μ in the respective energy bins, and image data generating means that generate as image data whose pixel values are the pixel data, data of an average absorption value image, characterized in that the pixel data calculating means is configured to calculate the pixel values based on a formula of: pixel value = t ⋅ a 1 ⋅ μ 1 +... + a n ⋅ μ n / n wherein a 1 to a n ·denote weighting coefficients of positive real numbers of 0 or more and the weighting coefficients meet a condition of a 1 +...+a n =n. information acquiring means obtains imaginary attenuation values μ im (t) * t and calculated linear attenuation values μ io (t) * t corresponding to the monochromatic X-rays from the imaginary attenuation values μ im (t) * t by multiplying previously prepared correcting data C(t), and obtains information on a thickness t of the object and the average linear attenuation coefficients μ from the linear attenuations values μ io (t) * t, pixel data calculating means that calculates pixel data composed of pixel values each obtained by multiplying addition information by the thickness t, based on the information acquired by the information acquiring means, the addition information being obtained by mutual addition of the average linear attenuation coefficients μ in the respective energy bins, and image data generating means that generate as image data whose pixel values are the pixel data, data of an average absorption value image, characterized in that the pixel data calculating means is configured to calculate the pixel values based on a formula of: pixel value = t ⋅ a 1 ⋅ μ 1 +... + a n ⋅ μ n / n wherein a 1 to a n ·denote weighting coefficients of positive real numbers of 0 or more and the weighting coefficients meet a condition of a 1 +...+a n =n.