1. A speech recognition system, comprising: a word speech recognition unit that converts input speech to a recognition result word sequence by using a predetermined word dictionary for recognition, the word dictionary including word entries arranged in a predetermined order; a syllable recognition unit that converts the input speech to a recognition result syllable sequence; a segment determination unit that determines a segment corresponding to an unknown word in the converted recognition result word sequence; and an output unit that obtains a partial syllable sequence corresponding to the determined segment from the recognition result syllable sequence, determines an ordered position of the partial syllable sequence in the word dictionary on the assumption that the partial syllable sequence exists in the word dictionary, and displays on a display device one or more word entries in the vicinity of the ordered position in the word dictionary, together with the recognition result word sequence, wherein the output unit displays the recognition result word sequence after replacing the recognition result word sequence with the partial syllable sequence with respect to the segment determined by the segment determination unit, and the output unit highlights the segment corresponding to the unknown word.