1. A musical apparatus for creating a length of melody based on a plurality of given melody motifs, the apparatus comprising: a melody motif provider which provides a plurality of melody motifs; a melody motif locater which locates said plurality of melody motifs at a plurality of positions along the length of a melody to be created; and a melody fraction developer which develops each of said located melody motifs to make a developed melody fraction for each of the remaining positions other than the positions where said melody motifs have been located along the length of a melody to be created, said located melody motifs and said developed melody fractions in combination constituting the melody to be created.