1. An image component separation device comprising: means for separating more than one image components from more than one chest radiographic images inputted thereto, the image components respectively representing bone and soft tissues as predetermined components in a site to be examined of a human body, each chest 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 chest radiographic images; and band extracting means for extracting, from each of the chest radiographic images, an image component of a spatial frequency band corresponding to a thickness of the ribs of the chest of the human body, such thickness being fixed and preliminary known, wherein the component separating means carries out independent component analysis on the image components of the spatial frequency band extracted by the band extracting means to obtain separation factors for separating the more than one image components from the image components of the spatial frequency band and uses the separation factors as the predetermined weighting factors.