To shorten a time from the reception of NACK (negative acknowledge) to the completion of data retransmission in a radio communication system employing a TDD (time-division duplex) system.

A base station 12 employs two retransmission systems which are a first retransmission system retransmitting data through a communication channel and a second retransmission system starting to retransmit data in earlier timing than the first retransmission system through a control channel slower in transmission rate than the communication channel. The base station 12 includes a retransmission completion timing determination section 30 which determines whether the retransmission completion timing of the data by the second retransmission system is earlier than the retransmission completion timing of the data by the first retransmission system according to negative acknowledge for the data transmitted to the mobile station through the communication channel, and a retransmission system selection section 32 which selects one of the first retransmission system and the second retransmission system as a retransmission system for retransmitting the data on the basis of the determination result ny the determination section 30.