A display image is superimposed and displayed on an outside image in a preferred manner.An optical system superimposes a display image displayed on a display device onto an outside image, and leads the display image to an eye of an observer. A display control unit controls the display size and the display position of the display image on the display device so that the display image is displayed in an image superimposition region (a flat region) detected from the outside image. For example, the display control unit controls the display state of the display image in accordance with the state of the image superimposition region in the outside image. Also, the display control unit performs control to selectively display the display image in a line-of-sight region or outside the line-of-sight region in accordance with the line of sight of the observer.