1. A speech recognition method using machine learning, comprising: receiving a speech signal as an input, performing speech recognition to generate speech recognition result information including multiple candidate sentences and ranks of the respective candidate sentences; processing the multiple candidate sentences included in the speech recognition result information according to a machine learning model which is learned in advance and changing the ranks of the multiple candidate sentences to re-rank the multiple candidate sentences; and selecting a highest-rank candidate sentence among the re-ranked multiple candidate sentences as a speech recognition result.