To provide a digital demodulator capable of suppressing interference waves by automatic adjustment.

This digital demodulator is provided with three parts an analog I/Q signal generation part 1, a digital demodulation part 2, and an interference wave suppression adjustment part 3 by rough classification. The interference wave suppression adjustment part 3 detects the gain difference of common-mode components and quadrature components based on the input/output signals of a low-pass filter 25a inside the digital demodulation part 2 and the output of a double quadrature mixer 23a and adjusts the reference voltage of an A/D converter 21a inside the digital demodulation part 2 so as to reduce the detected gain difference. Thus, the gain difference of the common-mode components and the quadrature components is reduced and the interference waves mixed in base band signals are efficiently removed.