In a backlight which arranges light emitting diodes on a side surface of a light guide plate, even when the light guide plate is made thin by further reducing a thickness of the light guide plate and the light emitting diodes having a thickness larger than the thickness of the light guide plate are used, it is possible to manufacture the light guide plate with high accuracy in a short time. In a liquid crystal display device having a backlight which radiates light to a liquid crystal panel, LEDs are mounted on the light guide plate formed on the backlight as a light emitting element, a light radiation portion of the light guide plate is formed by molding by applying pressure and heat to a sheet-shaped resin, and a light incident portion of the light guide plate is formed by injection molding.