Using an ontology to perform an information search utilizing a meaning given to information on a network without being required to perform complicated operations for forming an inquiry sentence in conformity with the ontology.A pre-stage before a search engine provides an information search supporting system having a morpheme analysis section, a syntactic and semantic analysis section, and a conversion execution section which converts a natural language sentence on which syntactic analysis and semantic analysis have been performed into an inquiry sentence described in an ontology description language by referring to a case frame ontology dictionary in which are stored information indicating to which property in an ontology does the relationship among a predicate, a subject and an object in the natural language sentence correspond and the case frame of the natural language sentence in the property.