A client-server type network having at least two clients which execute the same kind of operation. The server and the clients are improved in order to realize addition or reduction in the number of clients. When the client is started, the fact that the client in under operation is recorded in the data base of the server. Since the addition of a client is automatically recorded in the server, the addition is easily facilitated. The server is provided with a client managing device for judging whether or not the client is under operation by polling. If the client is stopped due to a problem or the like, the fact is automatically recorded in the data base of the server. Therefore, it is also easy to eliminate the client from the data base of the server.