To provide a backlight device uniform in luminance and excellent in availability of the exit light of an LED.

The backlight device is equipped with a light transmission plate 10, a frame 10, a circuit board 16, a light source 27 attached to the circuit board 16, and a shielding sheet 19 disposed to cover the top of the light source 27, wherein the frame 10 is equipped with a first side wall 11 disposed in the position on the side opposite to the light source 27 with respect to the circuit board 16, second and third side walls disposed respectively in the positions corresponding to both ends of the circuit board 16 and bottoms 19 connecting the respective side walls and has a shielding sheet dash section 11b projecting upward toward the top surface 1 of the first side wall 11; one end 9a of the shielding sheet 19 is made to abut on the shielding sheet dash section 11b of the first side wall 11; one end 9a of the shielding sheet 19 is fixed to the top surface 11a of the first side wall 11; the other end 9b of the shielding sheet 19 is fixed to one end 18a on the light source side of the light transmission plate 18; and the circuit board 16 is held by the shielding sheet 19 and the bottoms 19 of the frame 10.