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 (100) maps a downstream allocation control information unit, which is addressed to a terminal (200), 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 (100), a control unit (102) establishes a scale of the PDCCH region, and a transmission region establishing unit (131) establishes, on the basis of a scale value established by the control unit (102), a mapping region to which the DCI is mapped within the R-PDCCH region and the PDCCH region.