1. An apparatus for automatically generating grammar for use in the processing of natural language, the apparatus comprising: a setting processor configured to set one domain as a target domain to be processed by an intention analysis system; a first extractor configured to extract a corpus relevant to the target domain from a collection of corpora and divide the corpus into sentences and tag the sentences; a classification unit configured to classify the extracted corpus into a domain action among one or more domain actions that correspond to the target domain; a class converter configured to convert one or more words included in the extracted corpus into classes; and a generator configured to generate a grammar based on the converted classes of the extracted corpus wherein one or more ungrammatical words or sentences are removed from the corpus.