In the course of the development of the "Hyper Hospital," a novel medical care system constructed in the computerized information network using virtual reality as its human interface, we devised a virtual reality world creating system which allows users to con figure the world interactively. The re-configuration of the virtual world was designed to be carried out without interruptions of activity and the world can continue to exist during the reconfiguration process. This facility comprises an important part of our Hyper Hospital system because one of our major goals of this proposal of the Hyper Hospital is to restore maximum freedom for patients in the medical care system. Discussion was given in the present study with respect to the basic requirements of the system to be realized, including discussions on the permission given to the participants of different levels, and means by which to modify the structure of the virtual world. A preliminary implementation was described following this general consideration. The developed prototype was shown to be practically suitable to the test of our virtual environment applied to realistic medical scenes.