A digital mixer including a plurality of signal processing channels, said digital mixer comprising: a display device capable of displaying graphics; a plurality of controls (424, 530-1 to 530-8, 535, 536) to be used for performing parameter setting; an assignment section (551 to 556) adapted to assign k channels, selected from among said plurality of signal processing channels, to individual one of said controls; a display control section adapted to cause said display device to display, as a base screen, (a) a selected channel screen displaying a plurality of parameters for a selected one of the channels and (b) a channel strip screen (600-1 to 600-8) displaying a plurality of parameters for each of the selected k channels to be displayed as a base screen, in accordance with selection by a user; a window opening control section adapted to open any one of a plurality of types of parameter windows in response to selection operation to select a desired one of the parameters which is displayed on the base screen, said plurality of types of parameter windows including (a) a one-channel window (900, 930) that displays, for a selected one of the channels, k or less parameters belonging to a same group as the selected desired parameter, each of the k or less parameters being assignable to any one of said plurality of controls and (b) a k-channel window (801, 1030, 1100) that displays, for each of selected k channels, a parameter of a same type as the selected desired parameter, each of the parameters for the k channels being assignable to any one of said plurality of controls; a window-switching control section adapted to, in accordance with a window switching instruction, close a currently-opened parameter window and opens a parameter window of a designated other type; and a parameter control section adapted to, in response to respective operation of said plurality of controls, control values of parameters assigned to the operated control in accordance with a type of the parameter window being currently opened. a display device capable of displaying graphics; a plurality of controls (424, 530-1 to 530-8, 535, 536) to be used for performing parameter setting; an assignment section (551 to 556) adapted to assign k channels, selected from among said plurality of signal processing channels, to individual one of said controls; a display control section adapted to cause said display device to display, as a base screen, (a) a selected channel screen displaying a plurality of parameters for a selected one of the channels and (b) a channel strip screen (600-1 to 600-8) displaying a plurality of parameters for each of the selected k channels to be displayed as a base screen, in accordance with selection by a user; a window opening control section adapted to open any one of a plurality of types of parameter windows in response to selection operation to select a desired one of the parameters which is displayed on the base screen, said plurality of types of parameter windows including (a) a one-channel window (900, 930) that displays, for a selected one of the channels, k or less parameters belonging to a same group as the selected desired parameter, each of the k or less parameters being assignable to any one of said plurality of controls and (b) a k-channel window (801, 1030, 1100) that displays, for each of selected k channels, a parameter of a same type as the selected desired parameter, each of the parameters for the k channels being assignable to any one of said plurality of controls; a window-switching control section adapted to, in accordance with a window switching instruction, close a currently-opened parameter window and opens a parameter window of a designated other type; and a parameter control section adapted to, in response to respective operation of said plurality of controls, control values of parameters assigned to the operated control in accordance with a type of the parameter window being currently opened.