Rule reasoner includes: a Rete network builder for receiving ontology, including ontology instance represented by triple and ontology schema defining classes and properties of the triple, and reasoning rule, building Rete network corresponding to the ontology and the reasoning rule, selecting clue pattern corresponding to wild pattern rule with reference to the ontology schema when reasoning rule having wild pattern is received, rewriting the wild pattern rule with reference to the clue pattern, and adding test node, alpha memory node, and wild rule node so that the rewritten wild pattern rule is incorporated; a Rete network implementer for generating reasoned triple by implementing the Rete network built by the Rete network builder or generating reasoning rule where the wild pattern rule is dynamically materialized; and a Rete network expander expanding the Rete network by inputting the new reasoning rule, generated by the Rete network implementer, to the Rete network builder.