A handoff system and method between different kinds of devices, an SIP server and an application method of the SIP server applied thereto. The handoff system between different kinds of devices includes a plurality of devices; a SIP server which requests a routing path update when a handoff request signal is input from a source device among the plurality devices, and getting a target device to participate in a current session; and a gateway which updates a predetermined routing path when a request signal for the routing path update is input, and transmitting data to the source device and the target device via the updated routing path.