The fall of Koryo Dynasty and the subseqeuent foundation of Yi Dynasty may count as the most crucial political event in the 14th century Korean history. If so, we may pose, $quot;What was the element which played the decisive role in determining the political course?$quot; Certainly different historical perspectives may focus on different elements but the author is inclined to single out among others $quot;Dopyounguisasa$quot;. And its function and role can be summarized as follows. First, $quot;Dopyounguisasa$quot; was at first set up as a special_consultative body dealing with important defense problems meeting once in a year or in a few years. However, as Koryo`s relations with Won Dynasty became close and complicated, it became a standing organization empowered with decision a king. Consequently, its structure and function was expanded first to manage economic and cultural affairs and finally to control all national problems. Second, the establishment of Yi Dynasty may be attributed to the collective power of $quot;Dopyounguisass$quot; rather than to the individual capacity of its founder Yi Sung-Kye. It played the most decisive role when the $quot;Old Force$quot; collapsed. Third, After Yi Dynasty came into existence, $quot;Dopyounguisasa$quot; remained the power center and the king was nothing but the executor of its decisions. Therefore it was evident that the return of power to the king was possible only by unusual means, which sped np the Rebellion of the Royal Prince.