Provided is a radio communication mobile station device which can reduce the number of blind decoding processes at a mobile station without increasing the overhead by report information. The device includes: a judgment unit (210) which judges a particular PUCCH to which a response signal corresponding to the downstream line data is to be allocated among a plurality of PUCCH, according to a CCE occupied by PDCCH allocated to a particular search space corresponding to a CCE aggregation size of the PDCCH to which allocation information destined to the local station is allocated among search spaces changing in accordance with the CFI value; and a control unit (211) which controls a cyclic shift amount of a ZAC sequence of the response signal and a block-wise spread code sequence according to a correspondence between CCE occupied by PDCCH allocated to a particular search space and a particular PUCCH resource, the correspondence changing in accordance with the CFI value.