Terminal apparatus and response signal mappiing method

A terminal apparatus that communicates with a base station, using some or all of a plurality of configured downlink component carriers, the apparatus comprising:

• a receiving section that receives downlink allocation control information portions transmitted through downlink control channels of the plurality of downlink component carriers and downlink data transmitted through a downlink data channel indicated by the downlink allocation control information portions;
• a generating section that generates a response signal based on success or failure in receiving the downlink data;
• and
• a mapping section that maps the response signal to an uplink resource, wherein
• upon receipt of at least one of the downlink allocation control information portions that corresponds to a second downlink component carrier other than a first downlink component carrier among the plurality of component carriers, the mapping section maps the plurality of response signals respectively corresponding to the plurality of downlink component carriers to first resources corresponding to the plurality of configured downlink component carriers, and
• upon receipt of only the downlink allocation control information portion that corresponds to the first downlink component carrier among the plurality of component carriers, the mapping section maps the response signal corresponding to the first downlink component carrier to second resources corresponding to the first downlink component carrier.