A backlight unit includes a light guide plate 16, LEDs 17, a chassis 14, a frame 13 and positioning members 30. The light guide plate 16 includes two edge surfaces that are light entrance surfaces 16b and a front surface that is a light exit surface. The LEDs 17 are arranged to be opposed to the light entrance surfaces 16b and in a portion of the light guide plate 16 except for four corner portions 16d of the light guide plate 16. The chassis 14 is arranged on an opposite side of the light guide plate 16 from the light exit surface. The frame 13 is arranged on a light exit surface side to have the light guide plate 16 and the LEDs 17 between the frame 13 and the chassis 14. The positioning members 30 are arranged on an inner surface of the frame 13 to be opposed to the respective four corner portions 16d of the light guide plate 16. Each of the positioning members 30 is in contact with an edge surface of the light guide plate 16 at each of the four corner portions 16d so as to position the light guide plate 16 in a plate surface direction. The positioning members are configured to slide to be away from the light guide plate 16 along the inner surface of the frame 13.