The invention relates to a method for performing a radio resource control (RRC) connection or reestablishment in a communication system using carrier aggregation (CA), and to a terminal device for same. The present invention involves acquiring information on an additional component carrier (CC) through system information in addition to the CC which is specified during cell selection or reselection, and enables the CC on which additional information is acquired to be usable during the RRC connection or reestablishment performed by user equipment, to thereby prevent loads from being concentrated on a specific CC.