A head-mounted display device includes a transparent display for projecting light toward an eye so that images, rendered based at least on the augmented reality contents and a color profile of the wearer, for overlap with real images. The device also includes an infrared light source and a mirror configured to reflect the infrared light and transmit a portion of visible light corresponding to the real images. The device further includes a sensor configured to detect infrared light reflected from the eye for determining a gaze direction of the eye. The infrared light reflected from the eye is transmitted through the transparent display and reflected by the mirror toward the sensor.