In an endoscope system, rays of different wavelength bands are sequentially projected toward a target site of a test subject, to obtain image signals from the reflected rays. Reflection spectra are calculated from the image signals and subjected to a multi-regression analysis in combination with absorption spectra of those objects which are relevant to the inspection, such as blood or hemoglobin in the target site, and absorption spectra of irrelevant objects other than the relevant objects, such as bile or staining materials. Spectral components of the irrelevant objects in the reflection spectra are determined through the multi-regression analysis, and are eliminated from the reflection spectra, providing second reflection spectra. A couple of images are produced and displayed on the basis of the first reflection spectra from which the spectral components of the irrelevant objects are not eliminated and the second reflection spectra.