1. An image component separation device, comprising: component separating means for separating more than one image components from more than one radiographic images inputted thereto, the image components respectively representing more than one predetermined components in a subject, each radiographic image being formed by radiation transmitted through the subject, each radiographic image representing degrees of transmission and attenuation through the subject of each of different patterns of radiation having different energy distributions, the component separating means separating the image components by calculating weighted sums using predetermined weighting factors for each corresponding pixel among the radiographic images, wherein the component separating means carries out independent component analysis on the radiographic images to obtain separation factors for separating the more than one image components from the radiographic images and uses the separation factors as the predetermined weighting factors, and the independent component analysis is carried out with using a model representing, as a predetermined function, mixing factors representing mixing ratios of the more than one image components in each of the radiographic images using a parameter obtained from at least one of the radiographic images, the parameter having a predetermined relationship with a thickness of each of the more than one predetermined components or a thickness of the subject at each pixel of the ratio graphic images.