“MADO Interface” is a tangible user interface consisting of a compact touch-screen display and physical blocks. “MADO” means “window” in Japanese, and MADO Interface is utilized as the real window into the virtual world. Users construct a physical object by simply combining electrical blocks. Then, by connecting MADO Interface to the physical object, they can watch the virtual model corresponding to the physical block configuration (shape, color, etc.) The size and the viewpoint of the virtual model seen by the user depend on the position of MADO Interface, maintaining the consistency between the physical and virtual worlds. In addition, users can interact with the virtual model by touching the display on MADO Interface. These features enable users to explore the virtual world intuitively and powerfully. Keywords MADO Interface, tangible user interface, mixed reality, 3D modeling, real-time interaction, bi-directional interface