A display device configured to emit image light to display an image, and a camera or an illuminance sensor as an external light sensor configured to sense external light are provided, and the camera or the illuminance sensor is positioned to overlap a visually transparent light-guiding unit forming a front-of-eye part of the display device in an emission direction of the image light. Thus, the direction of sensing the external light in the illuminance sensor and the camera is set correspondingly to the direction of the line of sight of the viewer and a state, where these are located in the proximity of the eye of the viewer, is maintained.