Provided are a base station, whereby the erroneous dete ction of control information can be reduced, thereby preventin g 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 re gion, which can be used for any of a downstream control cha nnel region and a downstream data channel region, or to a se cond resource region, which can be used only for the downstr eam control channel, so as to transmit the downstream allocat ion control information unit. In the base station (100), a co ntrol 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 (10 2), a mapping region to which the DCI is mapped within the R-PDCCH region and the PDCCH region.
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