Provided is a radio communication mobile station device which can accurately judge a CDD mode of an interference signal from other cell when using a CDD. In this device, a mode judging unit (110) specifies some data signals among data signals inputted from a demodulation unit (106) to be CDD channel estimation signals and measures SINR for each of the CDD channel estimation signals. The mode judging unit (110) judges a CDD mode of the interference signal from other cell according to a difference between average SINR of each pair of the CDD channel estimation signals formed by two CDD channel estimation signals. Moreover, when the mode judging unit (110) has judged that the CDD mode is SD-CDD, the mode judging unit (110) generates CQI corresponding to average SINR of all the CDD channel estimation signals.