Abstract: A base station includes a precoding processor that conducts the same precoding process on a control channel and a reference signal, a controller that sets a plurality of regions including a region in which the reference signal is placed and a region in which the control channel is potentially placed. Different precoding processes are used among different regions. A transmit processor uses resources in a region to transmit the control channel and the reference signal. A mobile station device includes a controller that sets a region on the basis of announced information from the base station device, a propagation channel estimator that averages propagation channel variation estimation values from a plurality of reference signals within the region, and a control channel detector that uses the averaged propagation channel estimation values to detect the control channel that includes control information addressed to the mobile station device.