A complex condition determination unit is provided, having an error-pulse switching determination unit which outputs, as error-pulse determination information, information indicating whether an accumulated value of the number of error pulses is equal to or greater than a predetermined error-pulse threshold value; a CNR (carrier to noise ratio) modulation scheme determination unit which outputs, as CNR determination information, a modulation scheme determined in accordance with CNR information indicating the CNR of the received signal; an RSL (receive signal level) modulation scheme determination unit which outputs, as RSL determination information, a modulation scheme determined in accordance with RSL information indicating the RSL of the received signal; and a complex modulation scheme determination unit which determines the modulation scheme for the transmission source, in accordance with the error-pulse determination information, the CNR determination information, the RSL determination information, and the modulation scheme of the received signal.