To provide a device and a method for display which can always display the respective display states of windows as indexes on a display screen even when the windows are all opened.

An interface circuit 2 is connected between a host computer 1 which outputs image information and a display device 3 which displays the image information on its display screen. This interface circuit 2 generates information for an automatic index display of an old window at an arbitrary position on the display screen when the old window is hidden behind a new window on the display screen of the display device 3 and when information indicating the index display is supplied for video signal from the host computer 1. The user of the system can grasp all of the display contents and never enters an information deficient state.