A network device includes: a QoS management unit that measures a quality of service when user data transfer is performed between wireless terminal devices via user transfer function units of a core system device that controls a network; a PDU session management unit that acquires information of sessions from a session management function unit of the core system device, the sessions having been established for user data transfer between the wireless terminal devices; a PDU session setting unit that determines whether or not to establish new sessions, based on the quality of service; a user-data transfer destination management unit that manages a group that is based on the new sessions and transfer destinations of user data in the new sessions; and a user-data transfer destination setting unit that sets, to the session management function unit, the transfer destinations of user data in the new sessions.