Non-linear functions to be used for automatically varying current values of parameters to be set, independently of each other, are prepared in corresponding relation to a plurality of parameter setting operator members, such as faders of a mixer. In response to an automatic setting instruction, such as a scene recall instruction, the current value of the parameter, to be set via each of the operator members, is caused to vary gradually toward a given target value with a characteristic based on a corresponding one of the non-linear functions. For example, the non-linear function is defined by a start offset for setting a delay in a start of the variation, and a fade time necessary for actually causing the parameter to vary up to the target value after the variation start. Processing of a predetermined type of event (e.g., GPI event) may be delayed to allow for a time delay that would result during execution of automatic setting processing of each parameter.