The Changdan in Korean music is a most important thing of components of music. And then it is most important concept in teaching Korean music at elementary, middle and high school. But now we teach students a part of all concepts in Changdan and the incorrect concept in Changdan comes into existence. Therefore it urge us to understand the essential concept in Changdan to teach the universal concept in Changdan which have been in existence since the Chos6n Dynasty. Consequently, we must teach students that concept in Changdan. According to studies of the concept in Changdan, it could be found that the name of Changdan is originated from `long and short` of Chinese character `)` and Changdan was in use for many meanings. Nevertheless, we are teaching students Changdan as only drumming pattern. But we should teach that the essential concept in Changdan is a `long and short in music`. This music means sounds in singing and playing an instrument but this music does not mean accompanied sound with a many instrument. I am going to talk about Changdan in singing and playing a musical instrument. On the other hand, the music of korean drum accompanied with in singing or playing a musical instrument is called ` Changdan in korean drum accompaniment`(shortly Changdan in accompaniment). Strictly speaking, we should decide that what pattern of `Changdan in accompaniment` has to be used in accordance with the Changdan in music. For that reason it is not `Changdaut in accompaniment` but `Changdan in music` that we must teach students first. The understanding and teaching `Changdan in music` also are needed with a view to modifying the wrong concept in Changdan and recovering the essential concept of Changdan. That is a quick way to comprehend the concept in Changdan correctly and could be a great help in understanding the music. Concludingly, teaching `Changdan` has signigicant value in a point of teaching universal, substantial concept of Changdan and making student understand critical factor of Changrinn in accompaniment. There are two things to be selected as the teaching contents of Changdan in music. One is the pattern of Changdan which is often used in music and the other is the function of Changdan.