When any one of a plurality of amplifiers has been selected in response to amplifier selecting operation, an amplifier Detail View of the selected amplifier is displayed, where corresponding parameters are displayed via elements of the amplifier Detail View. When any one of a plurality of groups has been selected in response to group selecting operation, a group Detail View of the selected group is displayed, where maximum and minimum values detected from among values of a parameter of individual amplifiers of the selected group are displayed via a band-shaped element of a corresponding fader element. In another example, where a hierarchical group is selected in a tree display section on a control screen, respective state information, including parameter values or states of parameters, of a plurality of amplifiers belonging to the selected hierarchical group is displayed in a state information section.