A speaker speed conversion system includes: a risk site detection unit (22) for detecting sites of risk regarding sound quality from among speech that is received as input, a frame boundary detection unit (23) for searching for a plurality of points that can serve as candidates of frame boundaries from among speech that is received as input and, of these points, supplying as a frame boundary the point that is predicted to be best from the standpoint of sound quality, and an OLA unit (25) for implementing speed conversion based on the detection results in the frame boundary detection unit (23); wherein the frame boundary detection unit (23) eliminates, from candidates of frame boundaries, sites of risk regarding sound quality that were detected in the risk site detection unit (22).