An automatic performance apparatus that can change the performance speed of desired sections in a piece of music automatically performed. The apparatus comprises a section designator for designating a specific section in the piece, a time evaluator for counting performance duration of the piece, a modifier for modifying either the duration of the specific section (or the duration of a section other than the specific section) by modifying the tempo of the automatic performance or duration of notes of the performance data so that the performance duration of the automatic performance becomes equal to the desired duration. Thus, the total duration of the piece is adjusted to the desired duration while maintaining the duration of the specified section (or the duration of the sections other than the specified section).