1. A method of generating a prosodic model for controlling a speech style, comprising the steps of: defining at least two friendliness levels; storing recorded speech data of sentences, the sentences being made up according to each of the friendliness levels; extracting at least one of prosodic characteristics for each of the friendliness levels from the recorded speech data, said prosodic characteristics including at least one of a sentence-final intonation type, boundary intonation types of intonation phrases in the sentence, and an average value of F 0 of the sentence, with respect to the recorded speech data; and generating a prosodic model for each of the friendliness levels by statistically modeling the at least one of the prosodic characteristics, wherein the prosodic model includes information comprises an “opening” speech act and sentence type, a “request-information” speech act and sentence type, a “give-information” speech act and sentence type, a “request-action” speech act and sentence type, and a “closing” speech act and sentence type.