A CPU functions as an acquisition unit and a derivation unit. The acquisition unit acquires a first radiographic image and a second radiographic image respectively generated by a first radiation detector and a second radiation detectors which are irradiated with radiation with first energy emitted from a radiation source in preliminary imaging before main imaging from a radiography apparatus in which the first and second radiation detectors are arranged in a direction in which the radiation is emitted. The derivation unit derives the composition of a soft part of a subject, using the first and second radiographic images acquired by the acquisition unit, and derives second energy of the radiation emitted from the radiation source in the main imaging according to the derived composition of the soft part.
