To improve success rates of connection to base stations in mobile stations, using multi-carrier transmission systems.

The base station 12 using an OFDMA system, which is one of the multi-carrier transmission systems. The base station 12 includes: a variable gain amplifier 37 for collectively adjusting a reception level of a signal received in a predetermined band so that the maximum value of a reception level of a signal received from a plurality of mobile stations is within a reception dynamic range of the base station 12; a reception level detection section 40 for CCH for detecting a reception level of a control signal received by a control channel defined in the band before adjustment by the variable gain amplifier 37; a connection request detection section 61 for detecting a connection request to the base station 12, based on the reception level of the control signal detected by the reception level detection section 40 for CCH; and a channel assignment section 63 for assigning one of a plurality of subchannels to the mobile station that has transmitted the connection request when the connection request detection section 61 has detected the connection request.

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