The controller changes the low vehicle speed region set volume according to an operational input to the volume control switch within a first volume setting range set up in advance when the volume control switch is operated in the low vehicle speed region, and changes the high vehicle speed region set volume according to an operational input to the volume control switch within a second volume setting range set up in advance when the volume control switch is operated in the high vehicle speed region. A lower limit of the second volume setting range is set higher than an upper limit of the first volume setting range. Thus, it is possible to accurately control the volume of the audio system and improve feeling of volume change.