A borderline extraction element 15 extracts a borderline B of adjacent vertebrae from an X-ray image on which multiple vertebrae are projected connected in a line. A vertebral area setting element 17 sets a area sandwiched by the adjacent borderlines B as a vertebral area and an area number is put to the respective vertebral areas L. When the vertebral areas are erroneously set up, a setup data erase element 21 erases the data of the vertebral areas L and the area number when the borderline is corrected. The setup data are erased, so that the borderline B can be shift-corrected to any location. A vertebral area setting element 17 resets the vertebral area L based on the location of the corrected borderline. Accordingly, the respective vertebral areas L are set up to the accurate locations and only the borderline B extracted to the wrong location is shift-corrected and the vertebral areas are reset. The work-burden to the operator for setting the vertebral area can be largely lessened.
