Wearable computers have been receiving a great deal of attention as a new computer device. The Open Air Exhibition research group for the World Exposition 2005 EXPO 2005) is focusing on this new device as a means of making effective use of the outdoor exhibition. Since the year 2000. We have performed annual experiments to evaluate the possibilities of the wearable computer. Also. in order to increase the popularity. the experimental system was constructed for targeting to the general, not to the laboratory use. Therefore the weight of prototype device is restricted to enable any person to carry it and it is designed to be less obtrusive. In this paper. we discuss the basic requirements of the system for the Open Air Exhibition which is acceptable to the general.