To prevent connection failure caused by erroneous insertion of a connector by making a mistake of the surface and the back of a power supply board.

A backlight device includes a chassis 22 having a rectangular bottom plate 22a at a plane view, LED boards 25 mounted on one plate surfaces on the bottom plate 22a, LEDs arranged on the other plate surfaces of the LED boards 25 while light emitting sides are faced to a side opposite to a plate-shaped section side, power supply boards 43 supplying power to the LEDs and preparing connectors on their portions, housings 57 arranged on the LED boards 25 and having connection openings wherein connectors 54 can be inserted along a plate surface direction of the power supply board and electrically connecting between the LED boards 25 and the power supply boards by inserting the connectors 54 into the connection openings, positioning holes 74b arranged on each portion of the power supply board 43, and positioning sections 74a arranged at locations overlapped with the positioning holes on the bottom plate 22a at a plane view while the connectors 54 are inserted into the connection openings.