1. A method of storing image data representative of at least one document containing figures in an electronic filing system, said system having means for the storing image data representative of at least one document and key-words each corresponding to the image data representative of at least one document, means for searching the image data representative of at least one document stored in the storing means in response to search information including a desired key-word, and means for outputting image data representative of at least one document corresponding to the desired key-word as a result of the search by the searching means, the method comprising the steps of: receiving vector data of figures contained in at least one document to be stored in said electronic filing system; converting said vector data into image data representative of said at least one document; and producing a key-word corresponding to said image data representative of said at least one document by extracting data indicating an attribute of said figures contained in said at least one document from said vector data.