A voice data processing apparatus which converts voice data to voice playback data by an OLA method to correspond to a set magnification of playback velocity, including a voice data block setting device which partitions the voice data to set a plurality of voice data blocks, a segment setting device which sets voice data segments to the voice data to correspond to respective voice data blocks, a segment adjuster which adjusts positions and lengths on a time base, of the voice data segments set by the segment setting device, and a voice playback data generator which combines the respective voice data segments adjusted by the segment adjuster so as to overlap each other along the time base thereby generating the voice playback data.