An endoscope system capable of transmitting an optical signal even if some dirt is adhered to or fitting misalignment is present at an optical connector is provided. An endoscope system 1 includes an image sensor, a transmission module 20 having a light emitting element 23 configured to convert an imaging signal into an optical signal and output the optical signal, a first optical fiber 21, a first optical connector 11 holding an end of the first optical fiber 21, a second optical connector 12 removably connected with the first optical connector 11, a second optical fiber 31 held by the second optical connector 12 and having a core diameter larger than that of the first optical fiber 21, a reception module 30 having a light receiving element configured to convert the optical signal into an electrical signal and output the electrical signal, lenses 26 and 27 to increase the beam diameter of the optical signal, and lenses 33 and 34 to collect the optical signal.
