A digital mixer comprising: an input interface; one or more processors; an output interface; at least a first display and a second display; and an operator, wherein the operator includes a mode switching button for switching between a first mode and a second mode, the first mode is a normal mode and the second mode is a full-screen mode, the mode switching button is set to the normal mode in a default state, and the one or more processors are configured, by reading and executing a program, to: cause a home screen to be displayed on the first display and the second display; cause parameter setting screens of audio signals of different channels to be displayed respectively on the first display and the second display when a user operation of parameter setting is performed and the mode switching button is in the normal mode; cause different parameter setting screens of an audio signal of a single channel to be displayed respectively on the first display and, in a linked manner, on the second display when the user operation of parameter setting is performed and the mode switching button is operated to switch to the full-screen mode; when a channel is changed during the full-screen mode, cause different parameter setting screens of an audio signal of the channel after the change to be displayed respectively on the first display and, in a linked manner, on the second display; and process an audio signal which is input from the input interface using a parameter which is set in the parameter setting screen, and output the processed signal from the output interface. an input interface; one or more processors; an output interface; at least a first display and a second display; and an operator, wherein the operator includes a mode switching button for switching between a first mode and a second mode, the first mode is a normal mode and the second mode is a full-screen mode, the mode switching button is set to the normal mode in a default state, and the one or more processors are configured, by reading and executing a program, to: cause a home screen to be displayed on the first display and the second display; cause parameter setting screens of audio signals of different channels to be displayed respectively on the first display and the second display when a user operation of parameter setting is performed and the mode switching button is in the normal mode; cause different parameter setting screens of an audio signal of a single channel to be displayed respectively on the first display and, in a linked manner, on the second display when the user operation of parameter setting is performed and the mode switching button is operated to switch to the full-screen mode; when a channel is changed during the full-screen mode, cause different parameter setting screens of an audio signal of the channel after the change to be displayed respectively on the first display and, in a linked manner, on the second display; and process an audio signal which is input from the input interface using a parameter which is set in the parameter setting screen, and output the processed signal from the output interface. cause a home screen to be displayed on the first display and the second display; cause parameter setting screens of audio signals of different channels to be displayed respectively on the first display and the second display when a user operation of parameter setting is performed and the mode switching button is in the normal mode; cause different parameter setting screens of an audio signal of a single channel to be displayed respectively on the first display and, in a linked manner, on the second display when the user operation of parameter setting is performed and the mode switching button is operated to switch to the full-screen mode; when a channel is changed during the full-screen mode, cause different parameter setting screens of an audio signal of the channel after the change to be displayed respectively on the first display and, in a linked manner, on the second display; and process an audio signal which is input from the input interface using a parameter which is set in the parameter setting screen, and output the processed signal from the output interface.