An endoscope system (1) wherein an optical measurement device (3) has: a measurement control unit (327a) for setting, on the basis of viewing light output instruction information for an endoscope light source device (5) from a control device (4), a first measurement period in which a probe light source unit (321) stops output of measurement light and the endoscope light source device (5) outputs viewing light, and a second measurement period in which the probe light source unit (321) outputs measurement light and the endoscope light source device (5) outputs viewing light, and controlling the probe light source unit (321) and a light-receiving unit (322) on the basis of the setting a normalization unit (327c) for normalizing the measurement result of the light-receiving unit (322) in the first measurement period using the measurement result of the light-receiving unit (322) in the second measurement period as a reference a computational processing unit (327d) for computing a return light of the measurement light from the measurement result of the second measurement period using the measurement result of the first measurement period normalized by the normalization unit (327c) and a characteristic value calculation unit (327e) for calculating a characteristic value relating to a biological tissue on the basis of the computation result of the computational processing unit (327d).Linvention concerne un système dendoscope (1) dans lequel un dispositif de mesure optique (3) comprend : une unité de commande de mesure (327a) pour régler, sur la base dinformations dinstruction de sortie de lumière de visualisation pour un dispositif de source de lumière dendoscope (5) provenant dun dispositif de commande (4), une première période de mesure dans laquelle une unité de source de lumière de sonde (321) interrompt la sortie de lumière de mesure, et le dispositif de source de lumière dendoscope (5) délivre la lumière de visualisation, et une seconde période de mesure dans laquelle
