Disclosed is an auxiliary diagnostic apparatus including: a vector input unit that reads a test vector which is a spectral property vector of a biological tissue targeted for a diagnosis; a multiple linear regression analysis unit that executes a multiple liner regression analysis for the test vector with a plurality of individual component vectors which are spectral property vectors of particular substances, and obtains an error vector which is a vector of a residual error component; and an indicator calculation unit that extracts a feature of the error vector, and, from the extracted error vector, calculates an indicator representing whether an affected area is included in the biological tissue targeted for the diagnosis and which type of affected area has a possibility of being included in the biological tissue.