VIRTUAL IMAGE DISPLAY APPARATUS, VEHICLE COMPRISING HEAD-UP DISPLAY APPARATUS COMPRISING VIRTUAL IMAGE DISPLAY APPARATUS, AND METHOD FOR VIRTUAL IMAGE DISPLAY

The present application discloses a virtual image display apparatus. The virtual image display apparatus includes a gaze monitor configured to detect a gaze direction of a user and determine a gaze point based on the gaze direction; a display device configured to output an image; a projection lens configured to project the image onto a depth plane corresponding to the gaze point; and a controller configured to control a focal length of the projection lens based on a change of the gaze point.