An SIR information extracting section 106 extracts SIR measured at a communication terminal from the received data, and a fluctuation amount calculating section 109 calculates a fluctuation amount of SIR between time at which the communication terminal has measured SIR and transmission starting time of DSCH data using a TPC command, and a transmission system determining section 110 adds the SIR fluctuation amount calculated in the fluctuation amount calculating section 109 to the SIR measured at the communication terminal and estimates SIR of DSCH data so as to determine an optimal transmission system of DSCH data according to the estimated SIR.