A receiving unit (2) receives a modulated signal resulting from modulating a carrier signal with a digital encoded train resulting from error-correction encoding a digital signal train. A demodulating unit (4) demodulates the digital encoded train from the received modulated signal. A decoding unit (8) decodes the digital signal train from the demodulated digital encoded train. The receiving unit (2) outputs a received-signal strength indicative signal indicative of the received-signal strength of the modulated signal. During demodulating, a bit error rate computing unit (18) of the decoding unit (8) computes a bit error rate. The received-signal strength indicative signal and the bit error rate are inputted to a control unit (14), and, on the basis of these inputs, it is judged which one of the receiving conditions defined by received-signal strength indicative signals and bit error rates, the current receiving condition corresponds to.