To provide an angle demodulating device and its method capable of generating a local oscillation signal whose frequency is stable, and performing stable demodulation by a direct conversion method.

An FM modulation signal is amplified, and mixed with a pair of first local oscillation signals whose phase difference is 90° by mixers 4I and 4Q, and converted into a pair of base band signals. The base band signals are mixed with a pair of second local oscillation signals whose phase difference is 90° by mixers 8I and 8Q after the DC components are cut, and the obtained signals are added to each other so that an IF(intermediate frequency) signal can be obtained, and the IF signal is detected. Also, one base band signal is transmitted to a local oscillator 11. The local oscillator 11 extracts the carrier components of an FM modulation signal from the base bang signal, and mixes it with the second local oscillation signal, and adjusts the frequency of the first local oscillation signal so that the frequency can be converged to a fixed rate with respect to the frequency of the signal obtained by mixing.