In an automatic arrangement apparatus, a melody of a part of an original musical tune is memorized in a melody memory (4), chord data of the original musical tune is memorized in a chord progression memory (5), and a rhythm pattern in a rhythm pattern memory (12) is selected in accordance with the style and composition of the original musical tune. At a timing of a note code of the selected rhythm pattern, a top-note, an additional tone, a bass part and a drum part are produced. The top-note is produced by referring to a top-note table stored in a top-note table memory (15) and corresponds with the chord. The additional tone is produced in accordance with the top-note and the chord on a basis of a voicing table stored in a voicing table memory (16). The top-note and additional tone can be selected at a continuous two-tone pair.