1. A speech recognition apparatus which recognizes input speech input to said apparatus, the input speech including plural recognizable units which have a shorter duration than the input speech, said apparatus obtaining a recognition unit corresponding to each recognizable unit and outputting final recognition results by successively connecting each obtained recognition unit, said apparatus comprising: speech period sensing means for detecting a speech period by sensing a beginning and an end of the input speech; duration training means for calculating a relationship between durations of recognition units by using influencing factors which influence the duration of the recognition units; duration estimation means for estimating a duration of each of the recognizable units within the input speech by using the speech period of the input speech detected by the sensing means and a duration relationship calculated by the training means; and matching means for matching a recognition unit to a recognizable unit to produce a final recognition result based upon durations estimated by the estimation means.