Provided is a communication system that can be normally and efficiently operated in the case where existing carriers and new carrier types coexist. A base station device and a communication terminal device are configured to perform communication in cells of legacy carriers LC1 to LC3 being existing carriers. When the base station device starts operating new carrier types NCT1 and NCT2, the NCT1 and NCT2 are associated with legacy carriers belonging to the same frequency band. For example, the NCT2 is associated with the LC2 or the LC3 and is not associated with the LC1. The legacy carriers LC1 to LC3 associated with the NCT1 and the NCT2 notify the communication terminal device of the information on the NCT1 and NCT2. This allows the communication terminal device to communicate with the NCT1 and the NCT2.