Abstract: An apparatus includes a device for generating plural recognition candidates from a user's utterance including a series of words and a device for screening the candidates to select a few appropriate series of words from the candidates. In selecting the appropriate series of words, various factors are taken into consideration. Those factors include evaluation of sentence structures, grammar, relation among words and dialogue topics, and situations surrounding the user. For example, a dialogue topic is first determined, and then a recognition dictionary that only includes words relating to the determined topic is dynamically restructured in the system. Words included in the series of words are recognized and determined with reference to the restructured dictionary. Thus, recognition errors are minimized and determination of a correct series of words is effectively performed.