To provide a technique capable of setting another path with leaving a normal path as it is as a transfer path for a packet, minimally stopping a change into an existing network in this case and minimally inhibiting even the labor of a management.

The packet to be made to flow through another path is encapsulated as an AinA such as an IPinIP packet in an IP network, and an IF for an IP router opposed to a packet transfer device mentioned later is forwarded into a network as a destination address. The packet transfer device 100 captures the packet in the case of a passage and sets the destination address so as to release an encapsulation by using an encapsulating releasing section 107 and forward the packet towards an original destination or further pass another packet transfer device by using a destination changing section 105, and achieves a multistage transfer. Since the packet transfer device 100 behaves as a bridge to a normal packet, the transfer device is fitted and managed easily.

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