the invention relates to speech speed conversion , and provides a speech speed converting device and a speech speed converting method for changing a speed of voice without degrading the voice quality , without changing characteristics , regarding a signal containing voice . the speech speed converting device includes : a voice classifying unit that is input with voice waveform data and a voice code based on a linear prediction , and that classifies the input signal based on the characteristic of the input signal ; and a speed adjusting unit that selects either one of or both a speed conversion processing using the voice waveform and a speed conversion processing using the voice code , based on the classification , and that changes a speech speed of the input signal using the selected speed converting method .