A backlight unit 12 includes LEDs 16, light guide plates 18, an air layer AR and a scattering structures. Each light guide plate 18 has a light entrance surface 34 and a light exit surface 36. The light entrance surface 34 faces the corresponding LED 16 and light from the LED 16 enters through the light entrance surface 34. The light exit surface 36 through which light exits is arranged along an arrangement direction in which the LED 16 and the light entrance surface 34 are arranged. The light guide plates 18 are arranged in a parallel layout so as to be parallel to the light exit surface 36 and perpendicular to the arrangement direction. The air layer AR is provided between the adjacent light guide plates 18 and has a refraction index lower than that of the light guide plates 18. The scattering structures are provided in side-edge surfaces 31a that are interfaces between the light guide plates 18 and the air layer AR. The scattering structures are configured to scatter light inside the light guide plates 18. With this configuration, uneven brightness is less likely to occur.