We claim:
1. A mobile communication system in which radio communications between a
mobile terminal (71) supporting an aggregate carrier and a base station (72) are carried out
by using carrier aggregation for aggregating a plurality of component carriers, the aggregate
carrier being made up by aggregating the plurality of component carriers,
the mobile communication system being characterized in that, the mobile terminal (71) supporting the aggregate carrier is configured to transmit, to the base station (72), capability information about carrier aggregation of the mobile terminal (71) supporting the aggregate carrier.
2. The mobile communication system as claimed in claim 1, wherein the capability information is information indicating a combination of frequency bands, each corresponding to component carriers capable of carrier aggregation.
3. The mobile communication system as claimed in claim 1, wherein the capability information is information indicating a number of component carriers capable of carrier aggregation.
4. The mobile communication system as claimed in claim 1, wherein the capability information includes uplink capability information and downlink capability information differing from the uplink capability information, the uplink capability information being adapted for an uplink radio communication directed from the mobile terminal toward the base station, and the downlink capability information being adapted for a downlink radio communication directed from the base station toward the mobile terminal.
5. The mobile communication system as claimed in claim 1, wherein the capability information is transmitted from the mobile terminal supporting the aggregate carrier to the base station in response to an enquiry from the base station.
6. A base station (72) that carries out radio communications with a mobile terminal (71) supporting an aggregate carrier by using carrier aggregation for aggregating a plurality of component carriers, the aggregate carrier being made up by aggregating the

plurality of component carriers,
the base station (72) being characterized by receiving capability information about carrier aggregation of the mobile terminal (71) supporting the aggregate carrier, the capability information being transmitted by the mobile terminal (71) supporting the aggregate carrier.
7. A mobile terminal (71) supporting an aggregate carrier, which carries out radio communications with a base station (72) by using carrier aggregation for aggregating a plurality of component carriers, the aggregate carrier being made up by aggregating the plurality of component carriers,
the mobile terminal (71) supporting the aggregate carrier being characterized by transmitting, to the base station (72), capability information about carrier aggregation of the mobile terminal (71) supporting the aggregate carrier.