PROBLEM TO BE SOLVED: To provide an endoscope system that can reduce a case where an image becomes dark even when an endoscope is in an analyte.SOLUTION: An endoscope system 1 includes: a light source part 2 for emitting illumination light an optical fiber 3 for guiding the illumination light and irradiating an analyte from the leading end a treatment device 21 for performing a treatment accompanied by light emission for the analyte a light detector 12 for detecting return light of the illumination light from the analyte and light due to an external factor other than the return light and a light control part 18 which, while the light due to an external factor is detected, maintains the amount of light emission of the illumination light from the light source part 2 at a specified amount when the treatment device 21 is operative, and reduces the amount of light emission of the illumination light to a level lower than the specified amount when the treatment device 21 is not operative.
