The terminal having received the MN RRC reconfiguration message may update source cell configuration information by using a delta scheme when reconfiguration information of the S-SN is in the SN RRC reconfiguration message. Moreover, at the same time, the terminal may receive candidate cell IDs, conditions, pieces of candidate configuration information of T-SNs, and store same in the terminal. The terminal may perform a compliance check of a given MN RRCreconfiguration and a source configuration of the SN, and condition/target cell configuration information for sCHO. When a result of compliance check of all configuration information has no problem, the terminal may store configuration information for the candidate cells, and then transfer an MN RRC reconfiguration complete message (or RRC connection reconfiguration complete message) to the MN (operation 9-55). The MN having received this message may transfer a base station change confirmation message (e.g., SgNB change confirm message) to the S-SN (operation 9-65). The SgNB change confirm message may include information on an sCHO candidate cell list (i.e., sCHO candidate cell IDs (sCHO reconfiguration IDs) transferred through the message of operation 9-50) of cells successfully added to the terminal, or cells, configuration information of which is updated. This information may correspond to a candidate ID, a PCI, a CGI, or a t-SN ID operating a corresponding cell for each candidate cell. In another embodiment, when a terminal satisfies a given condition to determine an SN change, performs sCHO for a corresponding determined target cell, and transmits a complete message (e.g., an SN reconfiguratoincomplete message), a target node (T-SN2) may transmit an sCHO success message to the MN, and the MN having received this message may transfer an SN change confirm message to the S-SN. In this case, the S-SN may additionally transfer an SN release request ack to the MN, and request release of context of the S-SN. In this case, an SN reconfiguration complete (operation 9-85) message may not be required. Instead, when the terminal transmits an SN reconfigurationcomplete message to corresponding T-SN2 or after the transmission is successful, the terminal may transmit an MN RRC connection reconfiguration complete message to the MN. This message may has the same role as a message transmitted in operation 9-70, and include the same content as the message. As methods of transmitting the message transmitted in operation 9-70, a method of transmitting the message when a condition is satisfied (i.e., when conditional PSCell change/addition is performed) and a method of transmitting the message of operation 9-70 after conditional PSCell change/addition is successfully performed may coexist. The above operation may be considered when a corresponding PSCell is to be added or changed according to satisfaction of a given condition in all cases of MN-initiated Pscell addition, SN-initiated Pscell change, and MN-initiated Pscell change.