A radiation image processing apparatus includes: a group processing unit classifying a plurality of metal markers into a first group relatively far from a detector and a second group relatively close to the detector based on the area of each image of the plurality of metal markers in a captured image; a marker classification unit classifying the plurality of metal markers based on the relative positions of the plurality of metal markers to on the image plane of the captured image for each of the classified groups; and a pair processing unit selecting the metal markers of the first group and the metal markers of the second group, of which the relative positions match each other, as a pair.