In a navigation system integrated with a diagnostic device, an arithmetic and control unit for diagnostic communication makes an inquiry to electronic control units, such as an engine control unit, a transmission control unit and a brake control unit connected a CAN, about data which is used for the diagnosis of trouble causes based on setting information stored in a memory through diagnostic communication. An arithmetic and control unit for navigation system receives messages responding to the inquiry to sift through the data to be collected based on the setting information in the memory and stores the collected information in a hard disk drive device. The setting information is updated by making an inquiry to an external center via a mobile communication network.