Radiation is irradiated to an object, and the radiation, which carries image information of the object, is detected at a plurality of positions for image recording, which are set at different distances from the object, a plurality of radiation images of the object being thereby acquired. The acquisition of the radiation images is performed by use of a plurality of two-dimensional detectors, such that the radiation, which carries the image information of the object, at a position for image recording, which is remote from the object, is detected with a two-dimensional detector having a sensitivity higher than the sensitivity of a two-dimensional detector for detecting the radiation at a position for image recording, which is close to the object.