1. An image component separation device, comprising: component separating means for separating bone and soft tissues as predetermined components from more than one radiographic images inputted thereto, the image components respectively representing more than one predetermined components in a site to be examined of a human body, each radiographic image being formed by radiation transmitted through the site to be examined of a human body, each radiographic image representing degrees of transmission and attenuation through the site to be examined of a human body 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 bone and soft tissues as predetermined 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 bone and soft tissues as predetermined 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 site to be examined of a human body at each pixel of the ratio graphic images.