An endoscope apparatus (10) includes an imager (22) that detects reflected and scattered light of illumination light radiated to an observation object to output an imaging signal, and an image processor (24) that generates an image signal from the imaging signal. The image processor (24) generates an emphasis image signal corresponding to narrow band light included in an emphasis wavelength range that includes, for an optical absorption spectrum of a diagnosis target substance present in the observation object (O), at least one of at least a maximum wavelength that takes at least a maximum value and a color-range largest wavelength that takes a color-range largest value that is a largest value of the optical absorption spectrum in any one color range of three color ranges, a first color range, a second color range, and a third color range, and a non-emphasis image signal corresponding to narrow band light included in a non-emphasis wavelength range that is a wavelength range that does not include the emphasis wavelength range.
