“Media” is an artifact that expands our creativity and intelligence. We have been studying the use of “Rich Media” to support creative and intelligent human activities. Specifically, for over ten years we have focused on the 3D space as one of “Rich Media” and developed many 3D sketch systems that support the design of 3D objects. However, their long-term evaluation has revealed that they are not used by designers in real fields. Even worse, they are treated as if they were just mere attractions in an amusement park. The fundamental problem is the lack of the indispensable function for 3D space. In this paper, we propose new design principles, “life-size and operability”, which make the 3D sketch system truly valuable for the designer. The new 3D sketch system is designed on the basis of “life-size and operability”, developed, and evaluated successfully.