Operational states of one or more operators employed in a vehicle are detected to generate operational information corresponding to the detected operational states. Also, one or more traveling states of the vehicle are detected to generate traveling information corresponding to the detected traveling states. There is provided a table storing correspondency between various operational and traveling information and various sound control information, and sound control information corresponding to generated operational or traveling information is obtained with reference to the table. Sound signal is generated on the basis of the obtained sound control information to auditorily inform a user of the vehicle of the operational or traveling state of the vehicle. Contents of the table may be changed as desired by the user. There may be provided a plurality of tables so that the user can select any one of the tables.