This paper examines A. G. Frank's views about 15th-19th Korea (Joseon Dynasty) in his Reorient. A. G. Frank recognized that Korea might have played a great role in the international relations of East Asia, but he did not write systematically about it and he did not treat Korea as an independent player in the history of East Asia. I think the greatest limitation to his re-interpretation of East Asia is in that he depends too much on China's and Japan's perspective. In order to overcome Frank's shortcomings regarding the history of Korea, first I examine what Frank recognized about the Joseon dynasty between 1400 and 1800. Next I compare Joseon's development to that of China and Japan between 1400 and 1800. Frank compared Europe and East Asia (mainly China and Japan) from three aspects of quantities (population, production, productivity, and trade), qualities (science and technology), and mechanism (economic and financial institutions). With this research we insist that Joseon should not be dismissed in 15th-19th East Asia. The reasons are as follows. First, Joseon between 1400 and 1800 had developed economically as much as China and Japan. Second, Joseon had played a great role in connecting China and Japan and had a positive influence on the development of Japan. So we need to reappraise Reorient's view about East Asia. Only when role of Joseon can be correctly estimated, the dynamics and diversity of East Asia can be properly understood.