Whether a breath sound is contained in a current frame is determined by using a characteristic that a breath sound is small in autocorrelation and large in cross-correlation. Specifically, a harmonic-wave-structure estimating unit finds autocorrelation on the basis of a frequency spectrum of the current frame. A cross-correlation estimating unit finds cross-correlation between the frequency spectrum of the current frame and a frequency spectrum of a previous frame containing a breath sound. A breath detecting unit compares a value of a constant multiple of a value of the autocorrelation with a value of the cross-correlation, and, when the value of the cross-correlation is larger, determines that a breath sound is contained in the current frame.
