Abstract: An illumination device for guiding light rays from a light-emitting diode (LED) module toward a light guide plate to thereby perform planar illumination is disclosed. The illumination device includes a printed circuit board with a plurality of LED elements attached thereto. The circuit board has two or more positioning bosses which are attached in the same process as that of the LEDs. While letting the positioning bosses be tightly coupled with corresponding holes provided in the light guide plate, the circuit board and the light guide plate are adhered and fixed together, thereby accurately retaining the positional relationship between the LEDs and the light guide plate.