This paper is going to analyze the birth myth of three nations, DAEHA․NAMJO․DAERI by the writer\'s Theory of the Functional System of the Divinity(神格機能體系論). This thesis is written in the purpose of examining the formational process closely, making its meaning clearly and reviewing the Theory to establish its theory. As a result of reviewing this formational process, it is proved that the DAEHA\'s the birth myth is based on the narrative structure of the Indian RAMAYANA and the Tibetan birth myth. The DAEHA\'s birth myth has been established by the addition of new motifs on the previously mentioned basis. The myths of BAEKGOOK(白國)․NAMJO․DAERI handed down to BAEKJOK(白族). Among them, the myth of BAEKGOOK(白國) has retained its original form of progenitor\'s myth and has been reconstructed under the influence of Buddhism. The myths of NAMJO․DAERI are based on the progenitor\'s myth of KOORYUNG(九隆) which share the common ground with the natives of WINNAN(雲南) and the Buddhist deific structure and tradition has been added onto them. The Theory of the Functional System of the Divinity has focused on the point that the birth myths of three nations are the birth myths of the Middle Ages. Consequently, the theory confirmed that the birth myths of the Middle Ages repeat the three functional defic structure of the Ancient birth myth. This structure is, otherwise, disjoint if the Buddhism does not act as the foundation. I have confirmed that the birth myth of Middle Ages succeed the three functional defic structure but differs from that of the Ancient in the functional aspects. In the birth myth of Middle Ages, the existence of Supreme god is emphasized, compared to the Ancient one. This results from the missionary will of the class in charge of the birth myth and the interests of the state power.