A base vector acquisition unit acquires a base vector based on spectral characteristics of a subject to be an identification object with spectral characteristics known, and a system spectral characteristics acquisition unit acquires a spectral characteristics of an image acquisition system including spectral characteristics concerning a color imaging system provided for image acquisition of subjects including the subject to be identification object, and spectral characteristics concerning illumination light used in image acquisition of subjects by the color imaging system. A calculation unit calculates weighting coefficient concerning the base vector for each wavelength area, from image signal composed of a plurality of color signals obtained in the color imaging system, the base vector and spectral characteristics of the image acquisition system. An output signal calculation unit calculates an output signal as identification result of the subject to be identification object based on the weighting coefficients.