Disclosed are a method and device for a terminal to join a multicast service. A method performed by a session management function (SMF) may comprise the operations of: receiving a join request message for a terminal to join a multicast service; transmitting, to an NF repository function (NRF), a discovery request message including a multicast/broadcast service (MBS) session ID related to the multicast service; receiving a discovery response message from the NRF in response to the discovery request message, the discovery response message including an MB-SMF ID mapped to the MBS session ID; acquiring, from an MB-SMF identified by the MB-SMF ID, information about an MBS session indicated by the MBS session ID; and notifying a radio access network (RAN), to which the terminal connects, of information related to the MBS session, on the basis of the acquired information.