A rear display displays a driver image of a driver to a rear occupant. An operational information acquisition unit acquires operational information for changing a size of the driver image displayed on the rear display. An image control unit changes the size of the driver image displayed on the rear display, on the basis of the operational information acquired by the operational information acquisition unit. A sound control unit controls, at a time of generating a synthetic sound by combining a spoken voice of the driver with a reproduced sound of an AV source, a sound-level ratio between the spoken voice of the driver and the reproduced sound of the AV source, on the basis of the size of the driver image displayed on the rear display. A rear speaker outputs the synthetic sound generated by the sound control unit toward the rear occupant.