A reverse proxy server relays data between a client terminal connected to an external network and a host computer installed in an internal network segment using a session ID. A management server, in response to a connection request from the client terminal to the host computer via the reverse proxy server, decides whether a connection to the host computer is permitted based on host PC data having a host PC name of the host computer and a service name distributable by the host computer, and notifies the reverse proxy server and the host computer of the session ID to start connection when the connection is permitted. The host computer sends service data with the session ID after receiving the session ID. The reverse proxy server sends the service data from the host computer to the client terminal, and in response to data from the client terminal, sends the data with the session ID to the host computer.