At least a part of the three-dimensional community space is divided into regions and the right to use a region is sold at a particular price to a user who wants to obtain it. A user having the right to use a region is allowed to build an element such as a building or a signboard in the region via an avatar. If an attractive signboard with high originally is built, the region in which the signboard is built and also nearby regions become popular. As a result, the economic value of such a region becomes high. If desired, a user is allowed to resell his/her region via auction.