Each time a predetermined type of note controlling performance data (e.g., note-on event data) is detected from among a series of performance data, deviation values for a plurality of channels, varying in deviation state among the channels, are set such that a control value of a predetermined tone characteristic (e.g., event generation timing), included in the note controlling performance data, is caused to vary among the plurality of channels. Then, values, obtained by causing the control value vary among the plurality of channels in accordance with the respective deviation values of the channels, are set as new control values for the corresponding channels. Then, for each of the channels, there is created note controlling performance data of the predetermined type having the corresponding new control value incorporated therein. A break of a phrase in performance data may be detected so that control can be performed per phrase.