A base station apparatus comprising: a transmitting section configured to transmit downlink data using a first component carrier and a second component carrier; a response signal receiving section configured to receive a response signal which is a block of bits that indicates a plurality of error detection results of the downlink data for each of the first component carrier and the second component carrier generated at a communication partner apparatus, the response signal being mapped, according to a table that shows a mapping rule, to a constellation point among a plurality of constellation points on an uplink control channel resource (PUCCH resource) selected from a plurality of PUCCH resources, each PUCCH resource having a plurality of constellation points, wherein according to the mapping rule, a maximum value of a difference between a number of PUCCH resources where one of the plurality of error detection results indicates ACK only or NACK only on all of the plurality of constellation points and a number of PUCCH resources where other one of the plurality of error detection results indicates ACK only or NACK only on all of the plurality of constellation points is one or zero and wherein when reception of the downlink data on the second component carrier failed, a combination of PUCCH resource and constellation point on which the response signal is mapped is same as a combination of PUCCH resource and constellation point on which the response signal for a downlink data transmitted using only the first component carrier is mapped; and a retransmitting section configured to determine necessity of retransmission based on the received response signal and retransmit the downlink data, characterised in that, according to the mapping rule, a number of PUCCH resources where any one of the plurality of error detection results indicates ACK only or NACK only on all of the plurality of constellation points is one or larger than one. a transmitting section configured to transmit downlink data using a first component carrier and a second component carrier; a response signal receiving section configured to receive a response signal which is a block of bits that indicates a plurality of error detection results of the downlink data for each of the first component carrier and the second component carrier generated at a communication partner apparatus, the response signal being mapped, according to a table that shows a mapping rule, to a constellation point among a plurality of constellation points on an uplink control channel resource (PUCCH resource) selected from a plurality of PUCCH resources, each PUCCH resource having a plurality of constellation points, wherein according to the mapping rule, a maximum value of a difference between a number of PUCCH resources where one of the plurality of error detection results indicates ACK only or NACK only on all of the plurality of constellation points and a number of PUCCH resources where other one of the plurality of error detection results indicates ACK only or NACK only on all of the plurality of constellation points is one or zero and wherein when reception of the downlink data on the second component carrier failed, a combination of PUCCH resource and constellation point on which the response signal is mapped is same as a combination of PUCCH resource and constellation point on which the response signal for a downlink data transmitted using only the first component carrier is mapped; and a retransmitting section configured to determine necessity of retransmission based on the received response signal and retransmit the downlink data, characterised in that, according to the mapping rule, a number of PUCCH resources where any one of the plurality of error detection results indicates ACK only or NACK only on all of the plurality of constellation points is one or larger than one.