Although three-dimensional figures are three-dimensional, they are generally studied in two dimensions, such as in textbooks and notebooks, and are therefore difficult for students to understand. In this study, we focused on three-dimensional figures in the field of education and thought that effective learning would be possible by combining MR technology. Therefore, we developed a three-dimensional figure learning support system for upper elementary school students and junior high school students using a three-dimensional virtual space. The basic idea of the system is to use Microsoft's HoloLens2 to display 3D figures in a 3D virtual space using MR, and to have users directly perform actions (holding, moving, cutting, coloring, etc.) in accordance with the problem. The results of an experiment conducted on 41 students (13 fifth grade elementary school students and 28 first grade junior high school students) showed that although the system was useful, it did not lead to much learning retention. However, the results of the questionnaire showed that the system is effective in making learning enjoyable. It was also found that the system was easier to understand than the two-dimensional system.