An endoscope system 1 includes an insertion portion 5, a detection fiber 13 that transmits light received by a distal end face 13a, a beam splitter 28 that can divide the light transmitted by the detection fiber 13 into a first optical path and a second optical path, and guide the light, a detection fiber 14 that transmits light received by a distal end face 14a, a beam splitter 29 that can reflect the light transmitted by the detection fiber 14 into a third optical path oriented in the same direction as the first optical path and guide the light, and make light from an auxiliary light source 31 provided on a proximal end side of the detection fiber 14 incident on a proximal end portion of the detection fiber 14, detectors 47a to 47c that can detect light intensities of light from the first optical path and the third optical path, and an auxiliary image pickup device 30 that can receive light from the second optical path.
