To actualize a real-time display data transfer system which prevents the problem that the transfer capacity of a line is exceeded by one-sided transmission from a server side and the ineffective traffic and polling delay that a polling system has and is free of delay from the update of transaction data to the reception by a client.

A brand, etc., that the client desires to receive is previously registered on a server and when data on the brand are changed, the server notifies the client of the update; and then the client obtains the updated data from the server, so that real-time reception can be performed even through a low-speed line without issuing any ineffective command.