A base station which uses either one of a plurality of component carriers individually or uses an aggregate carrier which is an aggregate of the above-mentioned plurality of component carriers to carry out radio communications with a mobile terminal corresponding to the above-mentioned component carrier and also carry out radio communications with a mobile terminal corresponding to the above-mentioned aggregate carrier is provided. The base station notifies a bandwidth of an aggregate carrier which is an aggregate of all of the above-mentioned component carriers, as a bandwidth which the above-mentioned base station uses, to the mobile terminal corresponding to the above-mentioned aggregate carrier. As a result, while an improvement in the transmission rate is provided according to the aggregate carrier, the base station can also support an operation of a mobile terminal corresponding to a component carrier.