Provided is a radio communication device which can surely prevent inter-code interference while maintaining the use efficiency of an upstream line control channel and suppress separation characteristic of a response signal. The device includes: a control unit (209) which controls a cyclic shift amount of a ZC sequence used for a primary diffusion in a diffusion unit (214) and a Walsh sequence used for secondary diffusion in a diffusion unit (217) according to a PUCCH number inputted from a judgment unit (208); the diffusion unit (214) which performs primary diffusion of the response signal by the ZC sequence set by the control unit (209); and the diffusion unit (217) which performs secondary diffusion of the response signal by the Walsh sequence set by the control unit (209). The diffusion unit (214) performs primary diffusion of the response signal by using the ZC sequence having such a cyclic shift amount that the guard interval at the both ends of the detection window section is maximum in the ZC sequences having different cyclic shift amounts.