The liquid crystal display device is a liquid crystal display device having: a light guide plate for converting light from a light source into backlight for illumination; a first frame for containing the light guide plate; and a liquid crystal display panel provided over said light guide plate, wherein the liquid crystal display device further has a photosensor that is placed so as to face a sidewall of the light guide plate and detect an amount of the backlight, and the photosensor is placed so as to face the sidewall of the light guide plate through a hole or a notch created in a sidewall portion of the first frame.