An endoscope system 1 includes a head portion 4a, a connector portion 4c and a CCU 5. The head portion 4a includes a test signal generating portion 12 configured to generate a first test pattern signal. The connector portion 4c includes: a test signal generating portion 22 configured to generate a second test pattern signal which is a same pattern signal as the first test pattern a first comparison circuit configured to output a comparison result of comparing the first test pattern signal with the second test pattern signal and a test signal generating portion 24 configured to generate a third test pattern signal. The CCU 5 includes: a test signal generating portion 32 configured to generate a fourth test pattern signal which is a same pattern signal as the third test pattern and a second comparison circuit configured to output a comparison result of comparing the third test pattern signal with the fourth test pattern signal.
