A dialogue control system that uses an ontology that systematically expresses domain knowledge representing concepts and relationships between concepts to determine questions for a user and implements the questions, and implements a dialogue in accordance with received user answers. One or more dimension-classified ontologies and a basic ontology are stored, a concept from a user response is specified as a condition, and one or a plural number of the dimension-classified ontologies that meet the specified condition are fetched. The content of the fetched dimension-classified ontology/ies is overwritten on the basic ontology, in order according to dimension priorities from the dimension-classified ontology with the lowest dimension priority, and a multidimensional ontology is generated. The dialogue control system uses this multidimensional ontology to control the dialogue.