This invention provides a novel processing technique from customer authentication to order price claim in online sales of commodities and the like. First, upon receiving a customer authentication request from a shop computer, a first key is generated and transmitted to a customer terminal. Upon receiving the first key and authentication information for that customer, a legitimacy confirmation of the key and authentication processing are performed, and if both of the processing results are affirmative, a second key is generated and transmitted to the shop computer with an order identification number. In a case where the second key and shop authentication information are received from the shop computer, the legitimacy confirmation of the key, authentication processing of the shop, and credit processing of the customer are performed. If results of the aforementioned three processings are affirmative, content of the order is registered, and information indicating the registration of the order and so on is transmitted to the shop computer. After that, upon receiving an order price claim request from the shop computer, sales determination for the order is registered and the order price claim processing is carried out.