To always guarantee QoS for packet transfer and to achieve continuity of QoS guaranteed paths for upstream and downstream packet transfers between a mobile communications terminal and remote terminal, a transit router TR is used to detect any change of visitor location address reported via an existing QoS guaranteed path used for packet transfer and to newly set up a QoS guaranteed path according to the results of detection. Packets are transferred via existing QoS guaranteed paths until the transit router TR completes setup of a QoS guaranteed path. The mobile communications terminal and remote terminal are notified that the setup of the QoS guaranteed path is completed.