A method for transmitting a session initiation protocol (SIP) message by a user equipment (UE) in a wireless communication system, according to an embodiment of the present invention, comprises the steps of: establishing connection with a UE-to-network relay; and transmitting an SIP message to a proxy call session control function (P-CSCF) by means of the relay, wherein the P-CSCF corresponds to a P-CSCF address obtained by means of the UE-to-network relay or a P-CSCF address stored in the UE.