A radio terminal receives a directional multibeam from a radio base station and obtains each of correlation between orthogonal code series of the received directional multibeam and its own orthogonal code series to determine an orthogonal code series having the highest autocorrelation and further advertises orthogonal code series identification information identifying this orthogonal code series to the radio base station through an uplink physical channel. In comparison with a previous technique, this can shorten the time to be taken until the radio base station recognizes an orthogonal code series having the highest autocorrelation and a satisfactory reception condition in the radio terminal. Thus, it is possible to increase the speed of the loop control between the radio base station and the radio terminal, thereby improving the throughput of a channel to be used for the transmission of user data.