An endoscope system includes: an image sensor a transmission module a first optical fiber a first optical connector a second optical connector a communication mode stabilizing unit configured to smooth an optical beam a second optical fiber having a core diameter larger than a core diameter of the first optical fiber a reception module a first correction optical system including a first lens and configured to increase a beam diameter of an optical signal output from an end of the first optical fiber, and a second lens configured to convert the optical signal whose beam diameter is increased by the first lens into parallel light and a second correction optical system. The second optical fiber is a step index optical fiber, and the communication mode stabilizing unit smoothes the optical beam by using a larger area of a core of the first optical fiber.
