An in-vehicle system comprising: an autonomous driving system device that is mounted in a vehicle and implements autonomous driving of the vehicle; an autonomous driving controller that is configured to control the autonomous driving system device to perform a control related to the autonomous driving of the vehicle; a first network that connects the autonomous driving system device and the autonomous driving controller with a protocol conversion unit interposed therebetween so as to perform communication with each other by using a plurality of different protocols, the protocol conversion unit performing protocol conversion; a second network that connects the autonomous driving system device and the autonomous driving controller without the protocol conversion unit interposed therebetween so as to perform communication with each other by using a single protocol; wherein the autonomous driving system device includes an autonomous driving system operation device of which an operation is controlled by the autonomous driving controller to implement the autonomous driving of the vehicle, and an autonomous driving system detection device configured to detect information used for the autonomous driving of the vehicle and outputs the information to the autonomous driving controller; the first network connects the autonomous driving system operation device and the autonomous driving system detection device, and the autonomous driving controller with the protocol conversion unit interposed therebetween so as to perform communication with each other; the second network connects the autonomous driving system operation device and the autonomous driving system detection device, and the autonomous driving controller without the protocol conversion unit interposed therebetween so as to perform communication with each other; the in-vehicle system is configured to perform communication between the autonomous driving controller and each the autonomous driving system device by the second network, in preference to the first network that is separate from the second network; and the in-vehicle system is further configured to detect that communication using the second network does not work properly by comparing and collating information received by the autonomous driving controller through the first network with information received by the autonomous driving controller through the second network and to perform communication between the autonomous driving controller and each the autonomous driving system device by using the first network when it is detected that communication using the second network does not work properly. an autonomous driving system device that is mounted in a vehicle and implements autonomous driving of the vehicle; an autonomous driving controller that is configured to control the autonomous driving system device to perform a control related to the autonomous driving of the vehicle; a first network that connects the autonomous driving system device and the autonomous driving controller with a protocol conversion unit interposed therebetween so as to perform communication with each other by using a plurality of different protocols, the protocol conversion unit performing protocol conversion; a second network that connects the autonomous driving system device and the autonomous driving controller without the protocol conversion unit interposed therebetween so as to perform communication with each other by using a single protocol; wherein the autonomous driving system device includes an autonomous driving system operation device of which an operation is controlled by the autonomous driving controller to implement the autonomous driving of the vehicle, and an autonomous driving system detection device configured to detect information used for the autonomous driving of the vehicle and outputs the information to the autonomous driving controller; the first network connects the autonomous driving system operation device and the autonomous driving system detection device, and the autonomous driving controller with the protocol conversion unit interposed therebetween so as to perform communication with each other; the second network connects the autonomous driving system operation device and the autonomous driving system detection device, and the autonomous driving controller without the protocol conversion unit interposed therebetween so as to perform communication with each other; the in-vehicle system is configured to perform communication between the autonomous driving controller and each the autonomous driving system device by the second network, in preference to the first network that is separate from the second network; and the in-vehicle system is further configured to detect that communication using the second network does not work properly by comparing and collating information received by the autonomous driving controller through the first network with information received by the autonomous driving controller through the second network and to perform communication between the autonomous driving controller and each the autonomous driving system device by using the first network when it is detected that communication using the second network does not work properly.