A base station of a radio communication system including the base station and one or more mobile stations that communicate with the base station, the base station comprising: a receiver that is configured to receive, from each of the one or more mobile stations, a signal of a specific random access sequence selected from a plurality of random access sequence candidates; characterized by an identifier that is configured to: multiply each of the signals received by the receiver by each of weights, W, corresponding to a plurality of reception directions, calculate correlation values, p, of each of the multiplied signals and all random access sequence candidates and select a predetermined number of random access sequence candidates in a descending order of the correlation values for each of the multiplied signals, add for each of the plurality of random access sequence candidates the correlation values of the predetermined number of random access sequence candidates selected for each of the multiplied signals to thereby obtain a sum value for each of the plurality of random access sequence candidates, and identify the specific random access sequence and a receiving direction from the plurality of reception directions in which the signal of the specific random access sequence is received, based on absolute values of the sum values. a receiver that is configured to receive, from each of the one or more mobile stations, a signal of a specific random access sequence selected from a plurality of random access sequence candidates; characterized by an identifier that is configured to: multiply each of the signals received by the receiver by each of weights, W, corresponding to a plurality of reception directions, calculate correlation values, p, of each of the multiplied signals and all random access sequence candidates and select a predetermined number of random access sequence candidates in a descending order of the correlation values for each of the multiplied signals, add for each of the plurality of random access sequence candidates the correlation values of the predetermined number of random access sequence candidates selected for each of the multiplied signals to thereby obtain a sum value for each of the plurality of random access sequence candidates, and identify the specific random access sequence and a receiving direction from the plurality of reception directions in which the signal of the specific random access sequence is received, based on absolute values of the sum values. multiply each of the signals received by the receiver by each of weights, W, corresponding to a plurality of reception directions, calculate correlation values, p, of each of the multiplied signals and all random access sequence candidates and select a predetermined number of random access sequence candidates in a descending order of the correlation values for each of the multiplied signals, add for each of the plurality of random access sequence candidates the correlation values of the predetermined number of random access sequence candidates selected for each of the multiplied signals to thereby obtain a sum value for each of the plurality of random access sequence candidates, and identify the specific random access sequence and a receiving direction from the plurality of reception directions in which the signal of the specific random access sequence is received, based on absolute values of the sum values.