The invention concerns radiation image processing apparatus and cassettes for storing a radiation image. The apparatus includes a pixel-value analyzing section to analyze a pixel-value within a step pattern of a wedge area in which a density varies step by step, wherein the radiation image includes the wedge area; and a suspicious region analyzing section to detect a candidate of a suspicious region by using information outputted from the pixel-value analyzing section. Further, the suspicious region analyzing section includes a gradation-adjusting section to adjust a gradation of the radiation image on the basis of information, pertaining to the pixel-value, outputted by the pixel-value analyzing section. In addition, the suspicious region analyzing section also includes a parameter-adjusting section to adjust a parameter for detecting the candidate of the suspicious region on the basis of information, pertaining to the pixel-value, outputted by the pixel-value analyzing section.