A method of assembling a backlight unit equipped with a light source, a plurality of optical sheets, and a chassis into which at least the plurality of optical sheets are assembled, in which one of the plurality of optical sheets placed at a prescribed layer is treated as a first optical sheet and rest of the plurality of optical sheets placed following the first optical sheet are treated as second optical sheets, the method comprising:
- providing first identification parts of a same number as the second optical sheets at prescribed positions around the periphery of the first optical sheet in predetermined order, so as each of the first identification parts to specify a layer position where each of the second optical sheets is to be placed;
- providing a second identification part, on each of the second optical sheets, at a position corresponding to one of the first identification parts based on the layer position where the second optical sheet is to be placed;
- and
- placing the first optical sheet, and then superposing each of the second optical sheets so that each of the first identification parts is paired with the second identification part corresponding to the layer specified by the first identification part.