1. A speech recognition system, comprising: a word speech recognition section that converts input speech to a recognition result word sequence by using a predetermined word dictionary for recognition; a syllable recognition section that converts the input speech to a recognition result syllable sequence; a segment determination section that determines a segment that corresponds to a predetermined condition which is a ground for estimating an unknown word in the converted recognition result word sequence; and an output section that obtains a partial syllable sequence from the recognition result syllable sequence corresponding to the determined segment, and outputs one or more word entries which are in the vicinity of a position at which the partial syllable sequence is arranged in the word dictionary for recognition, in which words are arranged in the order defined for word entries, together with the recognition result word sequence.