An embodiment of the present description provides, in a situation in which, when a user equipment (UE) is roaming in a visited network, i.e. V-PLMN, the roaming is processed by means of a home routed (HR) mode and is successfully registered to H-PLMN IMS and a service is received, a method for performing authentication/registration of a UE, which is to receive an emergency service, if IMS-NNI does not exist between H-PLMN and V-PLMN.