In a vehicular navigation system, “AT command +CIEV” is received from a cellular phone by a BLUETOOTH communications. The received “+CIEV” is determined to identify a phoning state (or call state) of the cellular phone. A sound corresponding to the identified phoning state is outputted via a speaker in a corresponding sound volume level stored in an external memory device. A sound volume level, which was finally set for a certain phoning state, is not continuously used as an initial sound volume level for a subsequent phoning state different from the certain phoning state. An incoming sound, dialing sound, calling sound, and communicating sound are individually outputted in appropriately set sound volume levels, which enhances usability of the navigation system for users.