For each of a plurality of music pieces, a storage device stores respective tone data of a plurality of fragments of the music piece and respective musical character values of the fragments. Similarity determination section calculates a similarity index value indicative of a degree of similarity between the character values of each of the fragments of a main music piece and the character values of each individual fragment of a plurality of sub music pieces. Each of the similarity index values calculated for the fragments of each of the sub music pieces can be adjusted in accordance with a user's control. Processing section processes the tone data of each of the fragments of the main music piece on the basis of the tone data of any one of the fragments of the sub music pieces of which the similarity index value indicates sufficient similarity.