To provide an illumination device that uses a side-radiating light-emitting diode and simplifies the positioning adjustment of the light-emitting diode against a reflecting mirror.

In the illumination device, the light radiated from a light source 1 having the light-emitting diode 11 is reflected from the reflecting mirror 2. The light-emitting diode 11 radiates light in the direction of crossing the optical axis of the reflecting mirror 2, and is disposed only on the optical axis of the reflecting mirror 2. The light source 1 is composed of the light-emitting diode 11, a fixing member 12 to fix the light-emitting diode 11 on, and an adjusting member 13 to adjust the position of the light-emitting diode 11 against the reflecting mirror 2. A columnar part 122 of the fixing member 12 is inserted through the through-hole 131 of the adjusting member 13. The light source 1 is inserted in the neck 21 forming a space inside the top of the reflecting mirror 2. The bottom 132 of the adjusting member 13 is made to abut the bottom 212 of the neck 21 of the reflecting mirror 2, thereby locating the light-emitting diode 1 at a predetermined position against the reflecting mirror 2.