The Joseon Dynasty was founded based on the national ideology of Confucianism and the Chu-tzu’s doctrines. King Sejong pursued to establish a firm Confucian country, succeeding King Taejong’s legacy as “a king who succeeds ancestors’ accomplishment.” At the time of King Sejong, the Joseon Dynasty pursued its confucian universalism while differentiating its ideology from that of China, considering differences not only in geographical and climatic conditions, but also in language and custom. Reorganizing various culture and institutions during the reign of King Sejong, I argue, needs to be understood as a process of harmonizing Confucian universalism and Joseon’s particularity. Some of the outstanding accomplishments under the auspice of King Sejong, such as the creation of Hunminjeongeum (訓民正音, Correct Sounds to Instruct the People), the documentation of the Chileongsan (七政算, Calculation of the Motions of the Seven Celestial Determinants), the development of Hyangyak, and the publication of Nongsa jilseol (農事直說, Straight Talk on Farming), can be noted as results of King Sejong’s efforts to accomplish Confucian universalism while considering the differences in general mood of society, climate, custom, and voice which come from topography (geographical features). King Sejong as a highest ruler led the policies of science and technology; he presented the direction of policy implementation; and with officials, he built up an educational institution which cultivated experts with practical capabilities on the job; he ordered to collect domestic and international books for their education; he also promoted active publication. King Sejong demonstrated his decisiveness in pushing ahead with policies in order to make his policies and plans work in practice as well. In conclusion, King Sejong had endeavored to establish a Confucian country by reorganizing laws, institutions, yeak (禮樂, rites and music), and culture, and in this process of reorganization, he established the standards for the Joseon Dynasty’s science and technology. Given these accomplishments, King Sejong became revered as a “Yaoshun (堯舜) of the East.”