PURPOSE: To prevent erroneous recognition on a multiwindow display device and to improve operability by changing the superposition of a window corresponding to a pointing by a fingertip.

CONSTITUTION: When it is Judged that the input of a touch panel 8 is the one within the window and also. it is a touch by the fingertip by an input control part 1, a client issues an image insertion request to move the windows 23-25 to a server when the input shows contact on a title bar in the window. Also, when it is the contact on a size change button in the window, the client issues the image insertion request to change the size of the window. When it is the contact on the window other than a top window 23, the client issues a plotting request to display the window on the top window 23 to the server, and the server instructs plotting to a plotting processor 2 based on the plotting request issued from the client.