A head mounted display system includes an infrared sensor generating an infrared image, an image processor measuring a position of a user pupil based on the infrared image and generating image source based on the position of the user pupil, and an organic light emitting display device displaying an image corresponding to the image source. The organic light emitting display device includes a display panel and a panel driver. The display panel includes a plurality of infrared pixels disposed in an infrared emission region, the infrared pixels emitting infrared light, and a plurality of display pixels disposed in a display region, the display pixels emitting visible light. The panel driver provides driving signals to the infrared pixels and the display pixels.