A problem inherent to radiographic images, which may occur when an independent component analysis technique is applied to energy subtraction carried out on radiographic images, is solved to achieve separation of image components to be separated with higher accuracy. As preprocessing for an independent component analysis unit (22), a medium frequency component extracting unit (21) extracts a spatial frequency band which contain the components to be separated, a subset classifying unit (24) classifies pixels of the radiographic images into more than one subsets for each radiographic image based on a value of a predetermined parameter, and/or a nonlinear density conversion unit (26) applies nonlinear pixel value conversion to the radiographic images based on a value of the predetermined parameter. Alternatively, a nonlinear independent component analysis unit (25) carries out nonlinear independent component analysis according to a model using the predetermined parameter.
