A server system has stored therein a plurality of electronic transaction procedures corresponding to elements or combinations thereof including means of payment settlement of a purchased commodity, amount of deal, contents of the purchased commodity, financial institutions for making the settlement and so on. The server system selects one of the electronic transaction procedures corresponding to elements or a combination thereof, including means of payment settlement of a commodity to be purchased when a purchase-side client system requests a seller to sell the commodity. The electronic transaction procedure is distributed to the offer-side client, the purchase-side client and the settlement-side client through a communication network. Each of the offer-side client, the purchase-side client and the settlement-side client executes electronic transaction processes according to the distributed electronic transaction procedure. Either all of the selected electronic transaction procedure is distributed from the server system to the client systems at a time or parts of the electronic transaction procedure are successively distributed to the client systems from the server system.