To perform high line control by considering the quality of information to be communicated in a communication system in which a client is connected to a server having plural lines through a public line and performs data exchange.

A task processing information transmission program which sequentially transmits information about processing at a client C to a server S is transmitted to the client together with document data transmitted from the server S to the client C. A task processing situation at the client C is sequentially transmitted to the server S by the task processing information transmission program. An access management process on the server S estimates the processing situation of each client that is currently connected based on the transmitted task processing situation of each client. And, a communication control process performs line connection control to each client based on the estimated processing situation of each client. Thus, it is possible to perform high line control by considering not only physical information such as simple transmission quantity but also even the quality of transmitted information.