Provided is an optical sensor mounting structure for use in image display device devices that can accurately measure the amount of light from a backlight by measuring leak LED light, without having to modify an image display panel module itself. In an image display device using an image display panel module in which a wire drawing port for drawing a wire from a backlight is formed in a panel sheet metal, an optical sensor mounting structure includes an optical sensor configured to measure leak light from the backlight and a positioning member (intermediate connector) positioning the optical sensor. The optical sensor is disposed near the wire drawing port and measures the leak LED light from the wire drawing port.