A smooth and seamless terminal switching guaranteeing continuity of communication at an application level is realized. A call control part for setting and managing a physical and logical transmission path between communication terminals, a session management part for managing establishment of data communication between the communication terminals, and a switching request processing unit for controlling interruption and resumption of a session are provided, wherein the switching request processing unit exercises a function to temporarily interrupt a session after receiving a session switching request signal from a communication terminal, a function to instruct the call control part to establish a call connection with a switch destination communication terminal, a function to establish a session with an application on the switch destination communication terminal, and a function to resume, after establishing the session, a session with a communication terminal of an opposite side.