1. A concept network display system for representing knowledge-based information in a combination of concept nodes and relation links, comprising: input means for inputting data to indicate a current concept; knowledge base storage means for holding said knowledge-based information; display means for displaying concepts stored in said knowledge base storage means; first means for controlling said display means to display a concept tree window for showing concepts in a hierarchical tree arrangement including a current concept indicated by said input means; second means for controlling said display means to display a superconcept window for showing a superconcept of said current concept; third means for controlling said display means to display a subnetwork window for showing at least one concept combined with said current concept in any of instance relation and generic relation; select means responding to an input of data via said input means for selecting a concept of said concepts displayed on one of said windows by said display means to designate the selected concept as a new current concept; and rewrite means responsive to said new current concept for rewriting said concept tree window, said superconcept window and said subnetwork window based on said new current concept.