To provide a demodulator that can adaptively control arithmetic accuracy of a digital signal processing section, on the basis of a propagation state of an orthogonal frequency division multiplex signal for reducing the power consumption.

A valid OFDM symbol is extracted from an input data memory 1, an FFT 2 applies OFDM demodulation to the symbol, an equalizer 3 applies channel estimation/equalization to the output of the FFT 2, and the result is fed to an error correction coding decoding device 4 and an S/N measurement section 5. The S/N measurement section 5 calculates an S/N, on the basis of the signal supplied from the equalizer 3, while the error correction coding decoding device 4 calculates metric processing on the basis of the signal supplied from the equalizer 3. An integrator 6 integrates the metric output from the error correction coding decoding device 4. An arithmetic bit word length setting circuit 7 supplies a control signal to set an optimum arithmetic bit word length to each processing section, on the basis of the supplied S/N and metric integral value.