In the present invention, a bone density measuring device repeatedly alternates, while scanning with an x-ray beam, between projecting low-energy x-rays and projecting high-energy x-rays. When processing a detected value array obtained thereby, an L interpolation value is computed on the basis of two L detected values which are adjacent to an H detected value of interest. A pixel value (bone density) is computed from the H detected value and the L interpolation value, according to DEXA. The pixel value is mapped to the H detected value acquisition location. It would be permissible to interpolate from two H detected values instead of the interpolation of the two L detected values.