Provided are a base station, whereby the erroneous detection of control information can be reduced, thereby preventing the degradation of the system throughput. A base station maps a downstream allocation control information unit, which is addressed to a terminal, to a first resource region, which can be used for any of a downstream control channel region and a downstream data channel region, or to a second resource region, which can be used only for the downstream control channel, so as to transmit the downstream allocation control information unit. In the base station, a control unit establishes a scale of the PDCCH region, and a transmission region establishing unit establishes, on the basis of a scale value established by the control unit, a mapping region to which the DCI is mapped within the R-PDCCH region and the PDCCH region.