In a base station (100), a division number calculating unit (103) calculates the division number of a PRB pair on the basis of a first number of REs capable of mapping an allocation control signal, a second number of REs capable of mapping signals other than the allocation control signal, and a reference value, which is the number of REs satisfying the reception quality request in a terminal (200) for the allocation control signal, in each PRB pair. Then, a control signal mapping control unit (104) determines a search space by determining a control channel element group constituting a plurality of mapping unit resource region candidates within a CCE group obtained by separating each PRB pair contained in a first group into the same number as the division number.