A data modifying apparatus having: a memory that stores modification data for modifying data; a detecting unit for detecting each data group from performance data, the data group being unable to be reproduced at the same time from the viewpoint of music; and a modifying unit for modifying the data group detected by the detecting unit to divide the data group into a plurality of sub-data groups capable of being reproduced at the same time from the viewpoint of music, by using the modification data.