This study is to analyze and reconsider the meaning of the evaluation that Gabinja (甲寅字) was the “masterpiece” of metal type printing technology in the early Joseon Dynasty. During the reign of King Sejong, Several types were cast at Jujaso (鑄字所). Among them, Gyeongjaja (庚子字) achieved a kind of technological innovation that improved the problems of Gyemija (癸未字). Gyeongjaja changed the method of type casting and the method of typesetting. After that, the Gabinja was slightly larger in size than the Gyeongjaja. In addition, only the font of the type has changed, but there is no significant change on the surface in the method of type casting or typesetting. Nevertheless, not only the contemporaries but also the later generation appreciated Gabinja as the masterpiece of Joseon metal type printing technology. While seeking for the reasons for the high appreciation of Gabinja, this study argues that the achievement of Gabinja can be found in the establishment of a system for metal type printing. As a result, King Sejong’s Gapinja became a representative example of Joseon’s metal type printing technology.