A shopping server accepts a request for estimation of arbitrary designated items given by a client terminal, and generates estimation data for the designated items in accordance with the accepted request. The shopping server stores the generated estimation data at a shopping DB system. In response to retrieval of inventory status information for the items indicated by the estimation data stored in the shopping DB system, the shopping server updates the estimation data concerned in accordance with the retrieved inventory status information. The shopping server presents the updated estimation data to other client terminal in response to a request given by the client terminal which requested the estimation.