Document sharing system comprising: a document display support device; a plurality of terminals (2a, 2b, 2c, 2d), each of which has a display device; and a communication line connecting the display support device and the plurality of terminals (2a, 2b, 2c, 2d); wherein the document display support device comprises: a first processor configured to manage a shared document, respective partial regions of the shared document being displayed in three or more of the plurality of terminals as respective display regions; a first communication interface configured to perform communication between each of the three or more terminals and the document display support device through the communication line, so as to receive information corresponding to a display region of the shared document displayed in the display device of the respective terminal; and a memory configured to store at least information received through the first communication interface, said information corresponding to the display regions of the shared document for each of the three or more terminals; wherein the first processor is configured to identify based on the received information from two or more of the three or more terminals a common region, the common region being common to, out of the three or more terminals, the display region of the shared document in each of two or more terminals except one particular terminal, and the first processor is configured to inform said one particular terminal of the common region or a predetermined point of the common region through the first communication interface and wherein each of said terminals comprises: a second processor; and a second communication interface; wherein the second processor is configured to cause the display device to display at least a partial region of the shared document in accordance with operation performed by a user, the second processor is configured to inform the document display support device of information corresponding to a display region, of the shared document, displayed in the display device through the second communication interface, and the second processor is configured to update, when a point of focus is informed by the document display support device, a display on the display device in such a manner that a part corresponding to the point of focus appears. a document display support device; a plurality of terminals (2a, 2b, 2c, 2d), each of which has a display device; and a communication line connecting the display support device and the plurality of terminals (2a, 2b, 2c, 2d); a first processor configured to manage a shared document, respective partial regions of the shared document being displayed in three or more of the plurality of terminals as respective display regions; a first communication interface configured to perform communication between each of the three or more terminals and the document display support device through the communication line, so as to receive information corresponding to a display region of the shared document displayed in the display device of the respective terminal; and a memory configured to store at least information received through the first communication interface, said information corresponding to the display regions of the shared document for each of the three or more terminals; wherein the first processor is configured to identify based on the received information from two or more of the three or more terminals a common region, the common region being common to, out of the three or more terminals, the display region of the shared document in each of two or more terminals except one particular terminal, and the first processor is configured to inform said one particular terminal of the common region or a predetermined point of the common region through the first communication interface and wherein each of said terminals comprises: a second processor; and a second communication interface; wherein the second processor is configured to cause the display device to display at least a partial region of the shared document in accordance with operation performed by a user, the second processor is configured to inform the document display support device of information corresponding to a display region, of the shared document, displayed in the display device through the second communication interface, and the second processor is configured to update, when a point of focus is informed by the document display support device, a display on the display device in such a manner that a part corresponding to the point of focus appears. a second processor; and a second communication interface; wherein the second processor is configured to cause the display device to display at least a partial region of the shared document in accordance with operation performed by a user, the second processor is configured to inform the document display support device of information corresponding to a display region, of the shared document, displayed in the display device through the second communication interface, and the second processor is configured to update, when a point of focus is informed by the document display support device, a display on the display device in such a manner that a part corresponding to the point of focus appears.