[Problem] To mitigate effect of cervical vertebrae appearing in foretooth portion of dentition panorama image. [Solution] In step S5, a computer for calculation of an X-ray device loads a frame image f stored in memory at every kth index, and computes an average value of pixel values which denote brightness in the frame image f thus loaded as a pixel value average P. In step S6, the pixel value average P is used to compute a reference pixel value PC for all frame images f. In step S7, the reciprocal of each ratio per index k of the pixel value average P to the reference pixel value PC is respectively computed as a value R. In steps S8 and S9, the value R is corrected. In step S10, brightness-adjusted frame images are generated by respectively multiplying the pixel value of each pixel in the frame image by the index k-corrected value R, and a panorama image is built by overlapping the frame image generated per index k by a degree of shift corresponding to the index k.
