5. 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, a text feature vector is computed by said text feature vector generation unit; degree of similarity between a text feature vector stored in advance as speech information in said information storage unit and a text feature vector computed from said input speech 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.
5. 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, a text feature vector is computed by said text feature vector generation unit; degree of similarity between a text feature vector stored in advance as speech information in said information storage unit and a text feature vector computed from said input speech 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. 6. The information retrieval system according to claim 5 , wherein a text feature vector stored in advance in said information storage unit is a text feature vector generated by a text feature vector generation unit equivalent to said text feature vector generation unit.