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