An endoscope system includes: an elongated insertion portion insertable into a body cavity of a subject a first light source portion supplying illuminating light for illuminating an object in the body cavity of the subject an illumination fiber guiding the illuminating light supplied from the first light source portion and emitting the illuminating light to the object from an emission-end-side end face a light-receiving fiber group configured being provided with one or more optical fibers receiving, by incident-end-side end faces, return light of the illuminating light emitted to the object from the emission-end-side end face of the illumination fiber and an optical unit capable of causing either the illuminating light supplied from the first light source portion or predetermined light different from the illuminating light, which is supplied from a second light source portion different from the first light source portion, to be incident on an emission-end-side end face of the light-receiving fiber group.
