PURPOSE: To facilitate a cooperative work and to prevent the operation of an outsider by providing an access storage part and a data updating part and restricting an access right for a display device in a display controller controlling the display of plural work stations.

CONSTITUTION: The display controller 21 is provided with a video memory 23, a control part 22, the access storage part 24, etc. The video memory 23 stores the display data displayed in the display of the work stations 28 and 29. The access storage part 24 stores the input access right and the output access right from the work stations 28 and 29 together with ID of respective work stations 28 and 29. The content can be updated by the data updating part 26. The control part 22 refers to the access storage part 24 against an input/output request from the work stations 28 and 29. When access is available the input for the video memory 23 and the transfer of data on the video memory 23, etc., are executed.