1. A speech recognition apparatus comprising: an identification language model creation unit that selects, from learning texts for a plurality of fields for generating language models for the fields, a phrase that includes a word whose appearance frequency satisfies a set condition on a field-by-field basis, and generates an identification language model for identifying the field of input speech using the selected phrases; a speech recognition unit that executes speech recognition on the input speech using the identification language model, and outputs text data and a confidence for each word included in the text data as a recognition result; and a field determination unit that specifies a field that includes the most words whose confidences are greater than or equal to a set value based on the text data, the confidences of the words, and the words included in the learning texts for the fields, and determines that the specified field is the field of the input speech.