I introduce automatic music composition software using Markov chain. The automatic musiccomposition generates melody, chord and rhythm known as three elements of the music. In thesoftware, the melody is decided by 3-gram analysis and double Markov chain , and the chord is decided in original algorithm. This algorithm is called the downbeat-dependence method in this paper.As a result, I succeeded in creating a music composition that has characteristics very similar to the original. Furthermore, the type of chord in automatically-formed musical composition has been found to be greater than the number of the original music.