1. A speech recognition method, comprising: generating, by a processor, a word sequence based on a phoneme sequence generated from a speech signal; generating, by the processor, a syllable sequence based on the phoneme sequence, in response to a word element among words included in the word sequence having a lower recognition rate than a threshold value; and determining, by the processor, a text corresponding to a recognition result of the speech signal based on the word sequence and the syllable sequence, wherein the syllable sequence corresponds to the word element, wherein the generating of the syllable sequence comprises generating the syllable sequence by decoding a portion corresponding to the word element, among phonemes included in the phoneme sequence, and wherein the word sequence is generated by decoding the phoneme sequence and corresponds to at least the text corresponding to the recognition result of the speech signal.