A higher accuracy beam hardening correction with a low calculation load is performed with objects whose elements have a wider range of effective atomic numbers Zeff, thereby contributing to presentation of more quantitative X-ray images. Of two or more X-ray energy bins, two X-ray bins are selected to normalize X-ray attenuation amount μt in those bins such that one or more normalized X-ray attenuation amounts are obtained at each pixel areas. From reference information indicating a theoretical relationship of correspondence between the normalized X-ray attenuation amounts and effective atomic numbers of elements, one ore more effective atomic numbers are estimated every pixel area. Among the one or more effective atomic numbers (ZHigh, ZLow) and an effective atomic number (Zm) preset for the beam hardening correction, two or more atomic numbers are subjected to their equality determination.
