A communication system includes a vehicle exterior antenna, an electro-optic converter, and a multimode optical fiber. The vehicle exterior antenna transmits and receives an electric signal to and from a cloud system in the exterior of a vehicle. The electro-optic converter is connected to the vehicle exterior antenna and converts an electric signal received by the vehicle exterior antenna into an optical signal. The multimode optical fiber has a plurality of propagation modes for propagation of optical signals and connects the electro-optic converter and an on-vehicle device (an opto-electric converter, an on-vehicle router, and the like) in the interior of the vehicle.