A client is connected to a server for providing electronic commerce services in electronic commerce. An order is transmitted for a product in response to an input by a user to the server through a communications network. A trading identifier associated with the order and data on the contents of the order is received from the server, which is stored in a storage device. Associated trading processing information includes a present status of processing for processing initiated for the order, a present status of processing for delivery of the product corresponding to the order, a present status of processing for payment processing for the trading, and the trading identifier. During updating, a trading identifier is compared with trading identifiers included in the stored trading processing information, and a warning is output if they are not coincident. Updated trading processing information is added to the trading information stored in the storage device if they are coincident. The present status of processing for the processing initiated for the order, processing for delivery of the product corresponding to the order, and processing for the payment processing for the trading are managed until the order processing, delivery, and payment processing are completed.