20. The information retrieval system according to claim 16 , further comprising: a buffer unit for holding a speech recognition result obtained by said speech recognition unit; and a feature selection unit for selecting a speech recognition result from said buffer unit according to a prescribed feature selection rule, to be inputted to said degree of similarity computation unit; wherein said degree of similarity computation unit uses a speech recognition result selected by said feature selection unit to compute said respective degree of similarity.
20. The information retrieval system according to claim 16 , further comprising: a buffer unit for holding a speech recognition result obtained by said speech recognition unit; and a feature selection unit for selecting a speech recognition result from said buffer unit according to a prescribed feature selection rule, to be inputted to said degree of similarity computation unit; wherein said degree of similarity computation unit uses a speech recognition result selected by said feature selection unit to compute said respective degree of similarity. 23. The information retrieval system according to claim 20 , wherein said information registration unit for registering a set of text feature vectors or speech recognition results selected by said feature selection unit, as said speech information associated with information that is to be retrieved, in said information storage unit.