A melody segmentation module segments a given melody into a plurality of phrases. A phrase tonality analyzer determines a key of each phrase to provide a correct succession of keys of the melody. With this arrangement, the music apparatus can detect, from the melody, a modulation (change of key). A chord progression database is searched to assign an appropriate chord pattern to each phrase. Thus, the melody is harmonized with a natural and real chord progression. A style analyzer tests a melody phrase for a preselected music style and labels it with style-matched if it meets the preselected music style. A chord pattern characteristic of the preselected music style is selected from a chord progression database of the same music style to harmonize the style-matched phrase. Thus, the melody agrees with the harmonizing chord progression in terms of music style.