Communication system

The invention provides a communication system capable of reducing communication cost when transmitting a captured image of a moving body to the outside of the moving body. A communication system is provided with: an external communication unit that communicates via a first communication network with an external communication device located outside a mobile body; a communication relay unit that communicates with the mobile communication terminal via a second communication network and relays communication between the mobile communication terminal and the external communication device via the first communication network and the second communication network; and a communication control unit that executes a captured image transmission process in which the captured image captured by the camera is transmitted to the external communication device by the external communication unit, and a mobile communication relay process in which the captured image is transmitted to the external communication device by the external