Plural pieces of music data (performance data) each corresponding to each of plural music pieces are stored in a rewritable external storage device 25. Further, tone range restriction data indicating a sound generable range of a tone is stored in the external storage device 25 as associated with each piece of performance data or each piece of tone color data for controlling a tone color of a tone. A CPU 21 transposes the music piece corresponding to the selected performance data by the inputted transposition amount by the program process. In case where a part of the pitch of the transposed music piece is outside the sound generable range indicated by tone range restriction data corresponding to the selected performance data or to the selected tone color data, the transposition amount of all of or a part of the music piece including at least a note corresponding to the aforesaid part of the pitch is changed. Accordingly, a sound generable range is changed depending upon a music piece or according to a taste of a user even if a tone is generated with a same tone color.