PURPOSE: To provide a keyword extension retrieval system by which data can be retrieved even when the expression of a keyword is more or less different to each person.

CONSTITUTION: At the time of inputting a keyword from a terminal 2, a keyword extension processing part 3 prepares plural keywords whose meaning is the same and whose description is different from the inputted keyword. A retrieval processing part 4 retrieves the data from a data base 1 by the keywords prepared by the keyword extension processing part 3. The keyword is converted into the plural keywords by a prescribed conversion rule, and the data are retrieved from the data base 1 by the plural prepared keywords, so that the data can be retrieved by the keywords having the plural different description without using a synonym dictionary, or changing the existing data base.