A Business to Business electronic commerce (BtoB) system includes a message exchanging section, a task processing section and that conforms to BtoB standard specifications, and a difference processing section is added. For an outgoing business document, the difference processing section creates difference information between a past transaction and a new transaction within the range of the BtoB standard message format and sends the message to a business counterpart. For an incoming business document, the difference processing section restores a new transaction based on a past transaction and difference information.