A frequency-domain sample interval corresponding to a time-domain pitch period L corresponding to a time-domain pitch period code of an audio signal in a given time period is obtained as a converted interval T1, a frequency-domain pitch period T is chosen from among candidates including the converted interval T1 and integer multiples U×T1 of the converted interval T1, and a frequency-domain pitch period code indicating how many times the frequency-domain pitch period T is greater than the converted interval T1 is obtained. The frequency-domain pitch period code is output so that a decoding side can identify the frequency-domain pitch period T.