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; a processor configured to in a radiation image captured by exposing the object to radiation, for each unit region having one or two or more pixels, acquire the thickness of the object corresponding to the unit region, in the radiation image, for each unit region of the radiation image, acquire the thickness of the specific composition included in the object corresponding to the unit region, for each unit region of the radiation image, acquire 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 for each unit region of the radiation image, perform contrast correction using the acquired contrast correction amount of the unit region; and a frequency decomposition unit that performs frequency decomposition of the radiation image to generate a band image representing a frequency component of each of a plurality of frequency bands, wherein the correspondence relationship storage unit stores information indicating the correspondence relationship of at least one imaging condition at the time of capturing the radiation image, the thickness of the object, the thickness of a specific composition included in the object, and a contrast correction amount to each band image generated by frequency-resolving the radiation image, for each region corresponding to the unit region of each generated band image, the processor acquires a contrast correction amount to the band image corresponding to a combination of at least one imaging condition at the time of capturing the radiation image, the acquired thickness of the object for the unit region, and the thickness of a specific composition with reference to the stored information indicating the correspondence relationship, and for each region corresponding to the unit region of each generated band image, the processor performs contrast correction using the acquired contrast correction amount for the region and synthesizes all band images after correction to generate a processed radiation image.