1. A computerized method for constructing an endmember spectrum database stored on a computer, wherein said database stores endmember spectra of objects each formed of a plurality of substances, said method comprising steps performed by the computer of: obtaining a plurality of input endmember spectra from an input hyperspectral image; calculating a similarity between each input endmember spectrum included in the input endmember spectra and a spectrum of each substance stored in a spectrum library which stores spectra respectively of substances; calculating a similarity between each input endmember spectrum included in the input endmember spectra and each registered endmember spectrum already stored in the endmember spectrum database; and registering an input endmember spectrum that is included in the input endmember spectra and that is less than a predetermined value in all similarities, with the endmember spectrum database.