The system that can search patent documents more efficiently has been expected. Conventional retrieval systems have limitation in retrieval effectiveness because it is difficult to satisfy user's requests using only appearance frequency of words in a document. Thus we develop a method to enhance retrieval effectiveness by using patents' "References". And we also propose a method that allows us to see visually the difference of the importance of each retrieval keywords by plotting them on three different axes. To show how effective using "References" is, WG run a comparative experiment of 40 patent documents that we have analyzed using "References" and not using "References" on the view of seeing how much emphasis is given to featuring words. As a result of this experiment, we indicate the usefulness of our method.