Mobile IPv6 ensures a reachability of MN1 by adding a fixed home address to MN. When a user utilizes a Mobile IPv6 service, it is necessary that MN1 have a Mobile IPv6 function and the application support IPv6. However, the number of such MN1s is small. Besides, MN1 has no function that repetitively performs IPsec processing of transmitted/received packets. [MEANS FOR SOLVING PROBLEMS] A scenarioprocessing part (23) of MN1 includes means for selecting and executing a processing in accordance with a communication method when receiving a position registry response message of Mobile IP. Since the scenario processing part (23) has the means for selecting a communication method, it is easy to add a function to MN1. Moreover, since MN1 has the means for performing the IPsec processing a plurality of times, it is possible to provide a communication apparatus in accordance with a security management state.