A radio communication system includes a plurality of mobile station apparatuses and a base statement apparatus. Each of the mobile station apparatuses selects the lowest number and the second lowest number of control channel elements (CCEs) in which downlink allocation information is detected, and obtains two combinations, to be applied to transmission antennas, of a physical resource block (PRB), a cyclic shift amount, and an orthogonal code sequence in the time domain, on the basis of values by adding the numbers of CCEs to an offset value broadcast by the base station apparatus. Each of the mobile station apparatuses spreads pilot signals using spread codes based on the two combinations, arranges the spread pilot signals in PRBs corresponding to the signals, and transmits the signals through the transmission antennas.