By virtue of the characteristics inherent in diagrams, diagrammatic reasoning has potential and limitations that distinguish it from general thinking. It is natural that diagrams rarely appeared in Joseon mathematical books, which were heavily focused on computation and algebra in content, and preferred linguistic expressions in form. However, as the late Joseon Dynasty unfolded, there emerged a noticeable increase in the frequency of employing diagrams, due to the educational purposes to facilitate explanations and the influence of Western mathematics. Analyzing the role of diagrams included in Jo Taegu's 'JuseoGwangyeon', an exemplary book, this study includes discussions on the utilization of diagrams from the perspective of mathematics education, based on the findings of the analysis.