PURPOSE: To determine a retrieval range accurately by retrieving a pitch period where the retrieval range of the pitch period in each frame of the sound section except the first word head is limited near the pitch period detected in the past frame.

CONSTITUTION: Sound/non-sound discriminator 405 discriminates whether each frame has sound or not, and continuous sound sections and continuous non-sound sections are detected by detectors 407 and 408 respectively on a basis of discrimination signals. Then, busy discriminator 410 discriminates a busy state or non-busy state on a basis of continuous sound section information and continuous non-sound section information, and a fixed time interval is given to each frame by the first word head detector 411 on a basis of sound/non-sound information and busy/non- busy information. Then, integral-multiple pitch period error correction is performed in the first work head section by 413, and the pitch period which has a formant error corrected is extracted by 414, and the pitch period where the retrieval range of the pitch period in each frame of sound sections except the first word head is limited near the pitch period detected in the past frame is retrieved by 409. As a result, the retrieval range can be determined accurately.