Abstract: A system for implementing over the Internet a counter auction system which invites a large number of goods selling companies to compete for better goods prices on an online shopping forum. The joint purchase/sale information analysis unit on the Web server compares the conditions on the joint purchase program offered by the sellers based on the number of purchase reservations made by the Internet users who accessed the Web site and then puts the sellers under competition for a better condition on the joint purchase program of the commodities. The seller who offers the best selling condition is immediately given the right to sell its commodity. With this system, the purchasers can do the online shopping over the Internet in a short period of time and under good conditions.