To search related information even when the intention and viewpoint of a user are ambiguous and to search also unexpected information for the user.

An information storage part 101 stores information and the degree of association of each viewpoint of information. A viewpoint setting part 103 designates the criticality or the weighting factor of two pairs of viewpoints. Each of information relating part 104 and 105 synthesizes a composite viewpoint by linear and non-linear interpolations and further, calculates the composite degree of association based on each of the composite viewpoint and the degree of association of information. Each of the composite degree of association by a linear interpolation operation and a non-linear interpolation operation shows the degree of a normal relation and unexpectedness. A user can search desired information from the composite degree of association.