PURPOSE: To execute efficient information exchange by selectively using overlay data by purposes when plural pieces of the overlay data dealing with image data are provided.

CONSTITUTION: The overlay data meeting the purpose is read out of a memory means 2 and is displayed in superposition on the image data at the time of storing plural pieces of the overlay data having respective attributes into the memory means 2 and displaying the image data on a display means 4 via a multidisplay system 3. Arbitrary data is written via an input means 5 into the displayed overlay data and this data is stored and preserved via the multidisplay system 3 into the memory means 2. The required overlay data is selected by the purposes in this way and is immediately displayed on the display means 4 and, therefore, a user is able to make efficient information exchange with the opposite party.