A mobile communication system and method are disclosed for designating the resources to be used for mapping the control signal of HARQ performed by a base station apparatus. The base station apparatus and a mobile station apparatus communicate using a plurality of component carriers. The base station apparatus sets a single downlink component carrier for the mobile station apparatus and allocate, to the mobile station apparatus, a plurality of physical downlink shared channels by using a plurality of physical downlink control channels, which are mapped on the set downlink component carrier in the same subframe. The mobile station apparatus is designated, by the base station apparatus, a plurality of physical uplink control channels corresponding to the respective ones of the plurality of physical downlink control channels mapped on the set downlink component carrier, on a single uplink component carrier that corresponds to the set downlink component carrier.