Music piece data composed of audio waveform data are stored in a memory. Analysis section analyzes the music piece data stored in the memory to determine sudden change points of sound condition in the music piece data. Display device displays individual sound fragment data, obtained by dividing the music piece data at the sudden change points, in a menu format having the sound fragment data arranged therein in order of their complexity. Through user's operation via an operation section, desired sound fragment data is selected from the menu displayed on the display device, and a time-axial position where the selected sound fragment data is to be positioned is designated. New music piece data set is created by each user-selected sound fragment data being positioned at a user-designated time-axial position.