8. A pronunciation variation rule extraction method comprising: storing base form pronunciation data representing base form pronunciation of speech data; generating a sub word language model from said base form pronunciation data; recognizing said speech data by using said sub word language model; extracting a difference between a recognition result of said recognizing and said base form pronunciation data by comparing said recognition result and said base form pronunciation data; and controlling one weight value for said sub word language model, wherein said controlling includes outputting a plurality of said weight values, wherein said recognizing includes recognizing said speech data for each of said plurality of weight values, and wherein said controlling further includes determining whether or not said weight value should be updated, based on said difference when said difference is extracted.
10. The pronunciation variation rule extraction method according to claim 8 , wherein said controlling further includes updating said weight value, when said difference is larger than a predetermined threshold, such that said weight value is increased.