1. A radiographic image processing apparatus comprising: an image obtainment unit that obtains a radiographic image radiographed by irradiating a subject with radiation and by detecting the radiation passed through the subject by a radiation detector; a first information obtainment unit that obtains information about at least one of a radiography condition during radiography of the subject, a subject condition and detector characteristics, which are characteristics of the radiation detector; a second information obtainment unit that obtains body thickness information representing the body thickness of the subject; a target S/N setting unit that sets a target S/N of the radiographic image based on the body thickness information and information about at least one of the radiography condition, the subject condition and the detector characteristics; and an image processing unit that corrects the S/N of the radiographic image to the target S/N by performing, on the radiographic image, noise removal processing for removing noise.