A technology for preventing a driver from being distracted even if a navigation operates on an input device in the rear seat. A navigation system, connected to a combination of an output/input devices of a driver and to a combination of an output device and an input device of a fellow passenger, comprises a setting information storage unit storing setting information indicating whether or not information generated is to be output to the output device of the driver and an output processing unit, to the output device of the driver according to the setting information read from the setting information storage unit. When operation information enters from the input device of the fellow passenger, the setting information, stored in the setting information storage unit for the processing, changes to the information indicating that information is not output to the output device of the driver.