A fluorescence distribution image of each fluorescent agent can be acquired from a fluorescence image that has been captured in a mixed state so as to improve the diagnosability of cancer cells. An endoscope system comprises: a light source section for selectively irradiating two or more types of excitation lights having different spectral characteristics so as to excite two or more types of fluorescent agents having different optical characteristics; an imaging section provided on a part to be inserted into a body cavity, and having a light-receiving sensitivity in the wavelength bands of the two or more types of fluorescence radiated from the observation target by respective types of excitation lights; a storage section for storing relation information between the fluorescence intensity and the concentration of each of the fluorescent agents; a concentration information computing section for computing concentration information of each of the fluorescent agents on the basis of the fluorescence intensities of two or more images captured by the imaging section and the relation information stored in the storage section, and outputting the concentration information; and a mode switching section capable of switching between a first fluorescence observation mode in which at least one of the fluorescence intensity images acquired by the imaging section is presented, and a second fluorescence observation mode in which the concentration information of each of the florescent agents computed by the concentration information computing section is presented.