From the 13th century, Islamic culture began to be transmitted to Korea through the Mongol 蒙古 and Yuan 元 China, which governed Koryo 高麗 (918-1392) during the almost 100 years. Obviously, however, Islamic science and technology were deeply assimilated in the King Sejong period (1418-1450) of Joseon 朝鮮 (1392-1910), when a grand project for the calendar and instrument making was proceed. During this time, lots of astronomical and calendrical books including Islamic sources of Chinese version were imported from Ming 明 China, and researched by the court astronomers of Joseon. Moreover, astronomers and technicians of Korea visited China frequently for the study of astronomy and instrument making, and they brought back the new published books or useful information. As a result, Chiljeongsan Oeapieon 七政算外篇 which was a Korean edition of Islamic calendar, Huihui-li 回回曆 was published in 1444 with the Chiljeongsan Naepieon 七政算內篇 based on the Chinese calendar, Shoushi-li 授時曆. At the same time, in this process, many of Chinese and Islamic calendrical books were corrected by the Korean astronomers and reprinted by the new developed metallic type, Gabinja 甲寅字. In addition, astronomical instruments of Islamic influence such as water clocks with the automatic system, scaphe sundials, simplified armillary spheres etc. were re-made or newly modified in Korea. Also, it was known that there were many of inventions and innovations in astronomical and horological devices of this period. Consequently, through the great astronomical undertaking King Sejong reign, Korean science and technology were not only influenced by those of China and Islamic world, but also made remarkable improvement and progress.