A terminal apparatus comprising: a receiver which, in operation, receives first downlink assignment information indicating a resource for first downlink data allocated on a primary cell and receives second downlink assignment information indicating a resource for second downlink data allocated on another cell, and receives the first and second downlink data; a generator which, in operation, generates a plurality of response signals to the first and second downlink data; and a transmitter which, in operation, transmits the plurality of response signals characterized in that when the plurality of response signals to the first and second downlink data are transmitted with channel selection and the first downlink assignment information is received on a first control channel that is transmitted on a Control Channel Element, CCE, of a Physical Downlink Control Channel, PDCCH, region in the primary cell, the plurality of response signals are transmitted using one of a plurality of resources including a first resource determined from an index of the CCE of the PDCCH region and a second resource previously and explicitly notified by a base station, in accordance with a pattern of the presence or absence of reception errors of the first and second downlink data received; and when the plurality of response signals to the first and second downlink data are transmitted with channel selection and the first downlink assignment information is received on a second control channel that is transmitted on a Physical Downlink Shared Channel, PDSCH, region in the primary cell, the plurality of response signals are transmitted using one of a plurality of resources previously and explicitly notified by a base station including the second resource. a receiver which, in operation, receives first downlink assignment information indicating a resource for first downlink data allocated on a primary cell and receives second downlink assignment information indicating a resource for second downlink data allocated on another cell, and receives the first and second downlink data; a generator which, in operation, generates a plurality of response signals to the first and second downlink data; and a transmitter which, in operation, transmits the plurality of response signals characterized in that when the plurality of response signals to the first and second downlink data are transmitted with channel selection and the first downlink assignment information is received on a first control channel that is transmitted on a Control Channel Element, CCE, of a Physical Downlink Control Channel, PDCCH, region in the primary cell, the plurality of response signals are transmitted using one of a plurality of resources including a first resource determined from an index of the CCE of the PDCCH region and a second resource previously and explicitly notified by a base station, in accordance with a pattern of the presence or absence of reception errors of the first and second downlink data received; and when the plurality of response signals to the first and second downlink data are transmitted with channel selection and the first downlink assignment information is received on a second control channel that is transmitted on a Physical Downlink Shared Channel, PDSCH, region in the primary cell, the plurality of response signals are transmitted using one of a plurality of resources previously and explicitly notified by a base station including the second resource.