This paper describes a new interactive system for treating three dimensional objects. In this system, user's hand-writing actions and their records on a sheet of paper on a graphic tablet, and displayed information on a storage type CRT with the cursor function are the main man-machine communication routes. Users need not know internal data structure of models of objects. The internal information representation of the model is constructed and processed by user's actions on the external representation of the model, its record being consulted and updated by him. Output can take various forms of representation, which are made from the internal model, according to user's needs. The outlines of the software and the special hardware used in this system are described and examples of input and output are also shown.