An audio signal expansion and compression method for expanding and compressing an audio signal in a time domain, includes the steps of setting an initial value of a signal comparison length of a first comparison interval and a second comparison interval, used for detection of two similar waveforms in the audio signal, equal to or larger than a minimum waveform detection length, determining an interval length of the two similar waveforms while changing a shift amount of the first comparison interval and the second comparison interval so that the shift amount does not exceed the signal comparison length, and expanding or compressing the audio signal in the time domain on the basis of the interval length of the two similar waveforms.