1. A speech processing device comprising: an utterance error occurrence determination information storage unit configured to store utterance error occurrence determination information in which error patterns are associated with conditions of a word causing an utterance error; a related word information storage unit configured to store related word information including words, which are likely to cause a speech error, for each word that causes the utterance error, the speech error being an error in which, after a wrong word is completely or partially uttered, a correct word is uttered, or the speech error being an error in which the wrong word is uttered without any correction; a character string analyzing unit configured to linguistically analyze a character string and divides the character string into word strings; an utterance error occurrence determining unit configured to compare each of the divided words with the condition, give the error pattern to the word corresponding to the condition, and determine that the word which does not correspond to the condition does not cause the utterance error; and a phoneme string generating unit configured to generate a phoneme string of the utterance error corresponding to the error pattern in the word having the error pattern given thereto and generate a general phoneme string in the word that is determined not to cause the utterance error, thereby generating a phoneme string of the word string, wherein one of the error patterns associated with one of the conditions is the speech error, when the error pattern given to the word is the speech error, the utterance error occurrence determining unit further gives an incorrectly spoken word from the related word information, and the phoneme string generating unit generates a phoneme string of the incorrectly spoken word as the phoneme string of the utterance error corresponding to the error pattern of the word having the incorrectly spoken word given thereto.