To display the data on an online and the image data on a client on a display means with association secured between both data by retrieving a management file which records the data associated with the image data.

A host computer 1 has an online work program stored in a store means 11, and a store information acquiring means 14 retrieves the image data related to other data via a management file 13 and gives the information to the means 11. A client 2 has an optical medium storage device 4 storing the image data, and the means 14 retrieves the file 13 via a key input operation and sets the store information on the image data on a telegraphic message when the client 2 refers to the image data related to the data which are generated during the online work that is carried out with the computer 1. An image data display means 22 is started by an emulator 21 to retrieve the image data based on the store information and displays the image data on a CRT 3.