A mobile terminal apparatus that performs radio communication in a system band that is formed with a plurality of component carriers, the mobile terminal apparatus comprising: a demodulation section configured to demodulate downlink shared channel signals for the respective component carriers; a detection section configured to detect a state of each of retransmission acknowledgement signals of the respective component carriers based on the demodulated downlink shared channel signals; and an uplink control channel processing section configured to map the retransmission acknowledgement signals of the component carriers to an uplink control channel of a specific component carrier that is selected from the plurality of component carriers, wherein the uplink control channel processing section performs mapping based on a mapping table in which states of the retransmission acknowledgement signals of the component carriers are defined by bit information by phase shift modulation and selection information among a plurality of allocated resources for the uplink control channel, and in the mapping table, when a primary component carrier and a secondary component carrier of the plurality of component carriers are subject to one-codeword transmission, the number of allocated resources is set to two, and ACK, NACK and DTX, which are states of a retransmission acknowledgement signal of the primary component carrier are defined separately and DTX which is a state of a retransmission acknowledgement signal of the secondary component carrier is not defined separately, wherein for the secondary component carrier the DTX and NACK state is defined in the first allocated resource and the ACK state is defined in the second allocated resource. a demodulation section configured to demodulate downlink shared channel signals for the respective component carriers; a detection section configured to detect a state of each of retransmission acknowledgement signals of the respective component carriers based on the demodulated downlink shared channel signals; and an uplink control channel processing section configured to map the retransmission acknowledgement signals of the component carriers to an uplink control channel of a specific component carrier that is selected from the plurality of component carriers, wherein the uplink control channel processing section performs mapping based on a mapping table in which states of the retransmission acknowledgement signals of the component carriers are defined by bit information by phase shift modulation and selection information among a plurality of allocated resources for the uplink control channel, and in the mapping table, when a primary component carrier and a secondary component carrier of the plurality of component carriers are subject to one-codeword transmission, the number of allocated resources is set to two, and ACK, NACK and DTX, which are states of a retransmission acknowledgement signal of the primary component carrier are defined separately and DTX which is a state of a retransmission acknowledgement signal of the secondary component carrier is not defined separately, wherein for the secondary component carrier the DTX and NACK state is defined in the first allocated resource and the ACK state is defined in the second allocated resource.