A wireless communication base station apparatus that allows the number of times of blind decodings at a mobile station to be reduced without increasing the overhead caused by notifying information. In this apparatus, a CCE allocation part (104) allocates allocation information allocated to a PDCCH received from modulation parts (103-1 to 103-K) to a particular one of a plurality of search spaces that is corresponding to a CCE aggregation size of the PDCCH. A placement part (108) then places the allocation information in one of downstream line resources, reserved for the PDCCH, that is corresponding to the CCE of the particular search space to which the allocation information has been allocated. A radio transmission part (111) then transmits an OFDM symbol, in which the allocation information has been placed, to the mobile station from an antenna (112).