Abstract: A system and method provide a group purchase service in which a discount rate is applied differentially depending on the group purchase volume on first-come-first-served basis. In the group purchase service, a central server determines a discount policy such that each local server applies differential discount rates in group purchase rounds depending on group purchase volumes of an item in a purchase process performed by buyer devices. When each of the buyer devices accesses the local server in each service area and performs the purchase process for the item through the local server, the local server applies the differential discount rates to the rounds depending on the group purchase volumes of the item.