An allocation section 101 in a base station apparatus of the present invention sets the transmission rate of a transmit signal for a communication terminal apparatus based on a DRC signal transmitted from that communication terminal apparatus. A power margin information detector 117 detects power margin information from a demodulated signal generated by a demodulator 115, and, using that power margin information, a power setting section 118 makes a setting so as to give the minimum transmission power value at which received signal characteristics in each communication terminal apparatus meet the desired quality. Using the set transmission power value, the base station apparatus transmits a transmit signal of the set transmission rate to a communication terminal apparatus. By this means it is possible to suppress interference to a communication terminal apparatus that performs adaptive modulation communication with another base station apparatus and a communication terminal apparatus that performs adaptive modulation communication with the local base station apparatus at the same time.