1. A display control system, comprising: a document extracting device; and a portable information terminal, whereby the portable information terminal comprises: an identification information obtainer that obtains identification information which is assigned in order to identify an industrial machine; a serial information identifier that identifies, based on the obtained identification information, serial information which is assigned uniquely to the industrial machine; and a serial information transmitter that transmits the serial information to the document extracting device, the document extracting device comprises: a serial information receiver that receives the serial information from the portable information terminal; an extraction target identifier that identifies as an extraction target a portion of document information accumulated in advance, based on the serial information; and an extractor that extracts the extraction target from the document information; and that the portable information terminal further comprises a display that displays what is extracted by the extractor; and wherein the extraction target identifier comprises: a document information identifier that identifies a document associated with the serial information; and an extracted portion identifier that identifies a portion of the identified document regarding the industrial machine that is associated with the serial information as an extraction target and wherein the extractor extracts the extraction target from the document information and transmitting the extraction target to the portable information terminal.