PROBLEM TO BE SOLVED: To appropriately perform speech speed conversion, even when speech and a background noise are mixed. SOLUTION: The speech speed conversion device includes: a second level detection section 138 for detecting a level of a speech band included in a sound signal; a first level detection section 134 for detecting a level of difference from a right component and a left component of the sound signal; a speech speed conversion section 14 for converting a speech speed of the sound signal; and a speech speed conversion control section 139 in which the threshold is set larger, as the detected level of difference becomes larger, and which controls that the speech speed conversion section 14 performs speech speed conversion, when a detected level of a speech band is equal to a set threshold or larger, and it stops the speech speed conversion, when it is equal to the threshold or smaller. COPYRIGHT: (C)2010,JPO&INPIT