To display a window for displaying auxiliary information near a window for displaying main information. When a drag operation is performed to move a multiuser window to a predetermined position and display there, if the distance of the multiuser window to the main window when the drag operation is cleared is within reference value L_R and the distance of the top side of the multiuser window to the top side of the main window is within reference value H_R, then the multiuser window is automatically moved such that the side of the multiuser window comes in contact with the side of the main window and the top end of the multiuser window comes in alignment with the top end of the main window on a horizontal line.