3. The information retrieval system according to claim 1 , further comprising: a text feature vector generation unit for computing a text feature vector from a speech recognition result generated by said speech recognition unit wherein said degree of similarity computation unit is further to compute degree of similarity between two or more text feature vectors computed by said text feature vector generation unit; wherein, after performing speech recognition of said input speech by said speech recognition unit, respective text feature vectors are computed by said text feature vector generation unit, from a speech recognition result of said input speech and a speech recognition result stored in advance as speech information in said information storage unit; degree of similarity between each of said text feature vectors is computed by said degree of similarity computation unit; and said information selection unit selects information with which speech information having a high degree of similarity to input speech is associated, based on degree of similarity computed by said degree of similarity computation unit.
4. The information retrieval system according to claim 3 , wherein a speech recognition result stored in advance in said information storage unit is a speech recognition result generated by a speech recognition unit equivalent to said speech recognition unit.