A method for receiving a Vehicle to everything, V2X, message by a V2X communication apparatus of a subject vehicle, the method comprising: receiving a V2V message including Cooperative Adaptive Cruise Control, CACC, information from at least one CACC vehicle, wherein the CACC information includes CACC String ID, CSID, information for identifying a CACC string to which the CACC vehicle is belonged and string length management information used for managing a string length of the CACC string; obtaining the CSID information and the string length management information from the V2V message; and setting a value of the string length management information of the subject vehicle based on the CSID information and the string length management information, characterized in that the string length management information includes (i) Order In String, OIS, information indicating a current order of the vehicle supporting CACC in the CACC string, (ii) CACC String Lead Vehicle Position, CSLVP, information indicating a position of a lead vehicle in the CACC string, (iii) CACC String Length, CSL, information indicating a length of the CACC string for managing a length of the CACC string, and (iv) CACC String Length Limit (CSLL) information representing a limit of length of the CACC string, the limit of the length of the CACC string of the CSLL information represents one of (i) a total number of the vehicles supporting CACC which belongs to the CACC string and (ii) a geometrical distance between a lead vehicle and a last vehicle which belong to the CACC string, determining whether to join the CACC string to which the vehicle supporting CACC is belonged based on the string length management information, wherein, based on the limit of the length of the CACC string of the CSLL information representing the geometrical distance between the lead vehicle and the last vehicle which belong to the CACC string, whether to join the CACC string to which the vehicle supporting CACC is belonged is determined further based on (i) the CSLL information and (ii) the CSLVP information. receiving a V2V message including Cooperative Adaptive Cruise Control, CACC, information from at least one CACC vehicle, wherein the CACC information includes CACC String ID, CSID, information for identifying a CACC string to which the CACC vehicle is belonged and string length management information used for managing a string length of the CACC string; obtaining the CSID information and the string length management information from the V2V message; and setting a value of the string length management information of the subject vehicle based on the CSID information and the string length management information, characterized in that the string length management information includes (i) Order In String, OIS, information indicating a current order of the vehicle supporting CACC in the CACC string, (ii) CACC String Lead Vehicle Position, CSLVP, information indicating a position of a lead vehicle in the CACC string, (iii) CACC String Length, CSL, information indicating a length of the CACC string for managing a length of the CACC string, and (iv) CACC String Length Limit (CSLL) information representing a limit of length of the CACC string, the limit of the length of the CACC string of the CSLL information represents one of (i) a total number of the vehicles supporting CACC which belongs to the CACC string and (ii) a geometrical distance between a lead vehicle and a last vehicle which belong to the CACC string, determining whether to join the CACC string to which the vehicle supporting CACC is belonged based on the string length management information, wherein, based on the limit of the length of the CACC string of the CSLL information representing the geometrical distance between the lead vehicle and the last vehicle which belong to the CACC string, whether to join the CACC string to which the vehicle supporting CACC is belonged is determined further based on (i) the CSLL information and (ii) the CSLVP information.