To suppress not only stationary noise but also non-stationary noise.

An FFT(fast Fourier transform) part 11 converts an input signal (a1) from a time domain into a frequency domain in each frame. A siren sound suppression information setting part 12 detects the presence of a siren sound from the converted spectrum, outputs a siren sound presence flag, also extracts the fundamental frequency of the siren sound and outputs the fundamental frequency. A siren sound suppressing part 13 suppresses non-stationary noise by suppressing a fundamental frequency F1' and the r-th harmonic component of the frequency F1' from a spectrum G0(k) when the siren sound presence flag indicates 'presence'. An IFFT(inverse fast Fourier transform) part returns the output of the suppressing part 13, the non-stationary noise of which is suppressed to a time domain and outputs the output of the suppressing part 13.