Provided is an endoscope system that can accurately determine a transmission state based on a bit error rate and light receiving sensitivity, and thus is capable of coping quickly even when failure occurs in the transmission state. The endoscope system 1 includes an image sensor 10 configured to capture images of a subject, a first photoelectric sensor 11 configured to convert an imaging signal and test data output from the image sensor 10 into an optical signal and output the optical signal, an optical fiber 13 configured to transmit the optical signal output from the first photoelectric sensor 11, and an information processing device 3 including a second photoelectric sensor 20 configured to receive the optical signal transmitted through the optical fiber 13, a light amount measuring unit 22 configured to measure a receiving sensitivity of the test data converted into an electric signal by the second photoelectric sensor 20, a bit error rate measuring unit 26 configured to measure a bit error rate of the test data, and a determination unit 27 configured to determine a transmission state of the test data based on the receiving sensitivity and the bit error rate.
