1. An X-ray image processing system, comprising: an X-ray imaging device configured to obtain a plurality of consecutive divisional X-ray images along an examined body, each of the divisional X-ray images overlapping with one or more adjoining X-ray images of the other consecutive divisional X-ray images along a direction in which the divisional X-ray images were obtained; a memory configured to store X-ray image data of the plurality of consecutive divisional X-ray images, the X-ray image data including pixel values; an ROI setting unit configured to establish a region of interest (ROI) around inspection areas in overlapped edge portions of the adjoining X-ray images; an index value calculator configured to determine, for each of the overlapped edge portions, an index value based on the pixel values within the ROI; a gradation calculator configured to determine display gradations for the image data of the adjoining X-ray images, based on the index value; a gradation processing unit configured to correct the pixel values for the X-ray image data so that the display gradations of the image data of the adjoining X-ray images substantially coincides; and a continuous pasting operation unit configured to generate a continuous image by pasting together the X-ray image data of the altered pixel values.