3D computer graphics becomes a core technology for various applications such as scientific visualization, medical training and procedure, art, and entertainment. Geometric sense is a key skill for accurately understanding 3D information and designing relevant contents. We propose an electronic paper craft modeling system useful for fostering the basic geometric skill. The proposed system enables users to easily observe and manipulate regular polyhedron, the basic geometrical shapes found in various natural phenomena. 3D manipulations supported by the system give the users a feeling as if they are working with real paper craft model. Then, the system allows the user for gradually improving their skills for structurally analyzing the 3D virtual models. The paper elaborates the implementation method of the system and preliminary evaluation on how the proposed system can effectively support learning of basic geometry.