A base station communicates with a terminal, for which an uplink component carrier and downlink component carriers are configured. The base station adjusts a payload size of control information, transmitted in a downlink control channel, based on a basic payload size, and maps the control information onto a search space in at least one of the downlink component carriers. The basic payload size of the control information mapped onto a search space in a primary downlink component carrier is based on a number of information bits obtained from a bandwidth of the primary downlink component carrier, and on a number of information bits obtained from a bandwidth of the uplink component carrier. The basic payload size of the control information mapped onto a search space in a non-primary downlink component carrier is based on a number of information bits obtained from a bandwidth of the non-primary downlink component carrier.