By clearly separating knowledge of a specific area into a plurality of knowledge trees and organizing it, it is possible to describe systematic knowledge without fluctuation of notation.
Knowledge tree group management means that manages at least one knowledge tree, and knowledge entry management means that manages at least one knowledge entry existing for each of the knowledge trees are provided. Each of the knowledge entries includes a knowledge entry attribute description describing an attribute related to the knowledge entry and a knowledge entry parent-child relationship link describing a parent-child relationship with another knowledge entry of the knowledge tree. The knowledge entry attribute description includes a reference link to a knowledge entry belonging to a different or an identical knowledge tree or to an entry attribute description of the knowledge entry.