PURPOSE: To effectively use the frequency by measuring the bit error rate and reducing the error correction capability of error correction and encoding in the case of a low bit error rate to narrow the occupied band width.

CONSTITUTION: An error rate measuring part 17 measures the bit error rate; and if the bit error rate is low, it is judged that the condition of a propagation path is good, and the error correction capability of an error correction and encoding part 15 is reduced to correct and encode the error. Then the information transmission speed after error correction and encoding is made lower than conventional, and the occupied band width of the radio signal which is transmitted from an antenna 8 through a shared device 7 after information modulation, spectrum spread modulation, and frequency modulation is narrower than conventional. In a reception part 14, the inputted reception signal is subjected to frequency conversion, spectrum spread demodulation, and information demodulation and is decoded to the original information signal in an error correcting and decoding part 16 with the error correction capability reduced by the error rate measuring part 17.