Illuminating device, and liquid crystal display device and portable terminal device including the illuminating device

On the side surface of an optical guide plate, an engaging protrusion is formed for fixing the optical guide plate on to a frame by fitting the optical guide plate in a recessed portion formed on the frame. The light emitted from an LED enters the optical guide plate from a light-incident end surface and travels in the optical guide plate while spreading in a fan-shape. The engaging protrusion is formed outside the outgoing-angle range of the beam spreading in the fan-shape, thereby preventing occurrence of bright line caused by reflection of light at the corner portion of the base of the engaging protrusion.