When performing on-line shopping using the Internet, and when performing payment settlement for a product by a credit card, user's card data runs over the Internet, leaving the possibility of card data leakage, thereby causing a security problem. The user decides the product he or she wants to buy via a computer network (Internet) from a user system. Then, a transmission unit calls up a service center to send order data including the credit card data via a settlement network. Service center invoices the sales price to an approval center based on the order data. Approval center pays the price to service center. Then, service center sends the order data to the shopping system. A delivery processing unit then delivers the product to the user based on the order data.