An in-vehicle terminal sends a spoken voice as a voice signal to a relay server, and the relay server includes a voice recognition unit which converts the received voice signal into a string, and a control unit which searches for information stored in a main database or a temporary storage database by using the string and sends a search result to the in-vehicle terminal, and, upon searching for information stored in the main database, stores the search result in the temporary storage database. Upon receiving a voice signal, when the search result is stored in the temporary storage database, the control unit searches for information stored in the temporary storage database by using the string converted from the received voice signal, and, when the search result is not stored in the temporary storage database, the control unit searches for information stored in the main database by using the string.