1. A document filing system comprising: optical scanning means for scanning a plurality of documents randomly input thereto to produce document picture information; means for receiving and associating with each document a retrieval character code which is determined as a function of classification parameters, each retrieval code including a predetermined parameters, each retrieval code including a predetermined number of subcodes; memory means for storing a plurality of pieces of said document picture information and a plurality of retrieval codes corresponding thereto, each retrieval code including a predetermined number of subcodes; a display device having a display screen bisected into a first display region for exclusively displaying retrieval code data and a second display region for exclusively displaying the document picture image; retrieval code input means, manually operable by an operator, for specifying at least a portion of the retrieval character code; and retrieval controller means for, when a retrieval code is at least partially specified by an operator designating one or more subcodes thereof, (a) extracting from said memory means all of those retrieval codes which include the specified subcodes as a part thereof and the corresponding pieces of document picture information, in accordance with a predetermined algorithm, (b) causing said display device to exclusively display a list of the extracted retrieval codes on said first display region ot allow the operator to select a desired document while seeing the retrieval code list, said retrieval controller means, when the operator inputs the remaining subcode or subcodes through said input means to specify a certain document, causing said display device to display a picture information of the specified document on the second display region and to continuously display said retrieval code list on the first display region, whereby, after referring to the presently displayed document picture image, the operator may select another document from those satisfying the operator's earlier partial specification based on the retrieval codes continuously displayed on said first display region, thereby facilitating the operator to find his finally desired document whose picture information will be displayed on the second display region of said display device.