An endoscope system includes a head portion, a connector portion and a CCU. The head portion includes a test signal generating portion configured to generate a first test pattern signal. The connector portion includes: a test signal generating portion 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 configured to generate a third test pattern signal. The CCU includes: a test signal generating portion 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.
