1. A radiation image processing device comprising: a correspondence relationship storage unit that stores information indicating the correspondence relationship of at least one imaging condition at the time of capturing a radiation image, the thickness of an object in a radiation exposure direction, the thickness of a specific composition in the radiation exposure direction included in the object, and a contrast correction amount; an object thickness acquisition unit that, in a radiation image captured by exposing the object to radiation, for each unit region having one or two or more pixels, acquires the thickness of the object corresponding to the unit region; a composition thickness acquisition unit that, in the radiation image, for each unit region of the radiation image, acquires the thickness of the specific composition included in the object corresponding to the unit region; a correction amount acquisition unit that, for each unit region of the radiation image, acquires a contrast correction amount corresponding to a combination of at least one imaging condition at the time of capturing the radiation image, the acquired thickness of the object of the unit region, and the thickness of the specific composition, with reference to the stored information indicating the correspondence relationship; and a correction processing unit that, for each unit region of the radiation image, performs contrast correction using the acquired contrast correction amount of the unit region.