It is possible to provide a signal processing method and device capable of increasing the following speed of an estimated noise in a noise level rapidly increasing section and eliminating a noise spectrum estimation error by affect of audio in an audio section. A time region signal as input signal sampling data is extracted. For each of frames, the time region signal is converted into a frequencyregion signal to calculate an input spectrum. Furthermore, a minimal value of the input spectrum is obtained and a noise spectrum as a frequency region signal of the noise component contained in the input audio signal is estimated. Moreover, the input spectrum is compared to the noise spectrum to judge whether the section is a noise section or a mixed section of the noise and audio.