I introduce automatic music composition software using Markov chain. The automatic music composition generates melody, chord and rhythm known as three elements of the music. In the software, 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.