To prevent connection failure caused by erroneous insertion of a connector.

A backlight device includes a chassis 22 having at least a rectangular bottom plate 22a at a plane view, LED boards 25 wherein one plate surfaces are mounted on the bottom plate 22a, LEDs 24 arranged on the other plate surfaces of the LED boards wherein light emitting sides of the LEDs are faced to sides opposite to a bottom plate 22a side, power supply boards 43 for supplying power to the LEDs 24, connectors 54 arranged on the power supply boards 43 and having two terminals 56 arranged in parallel with each other, housings 57 arranged on the LED boards 25 and having connection openings 55 wherein the connectors 54 are inserted along a plate surface direction of the LED board 25 and electrically connecting between the LED boards 25 and the power supply boards 43 by inserting the connectors 54 to the connection openings 55, and projection members 70 arranged by adjoining in a direction wherein the housings 57 and the terminals 56 are arranged in parallel with each other and projecting from the bottom plate 22a to the light emitting sides of the LEDs 24 rather than the connection openings 55.