There is provided an illuminating device. The illuminating device includes a light source unit including a substrate and one or more light emitting devices mounted on the substrate, and a heat radiating unit including a sealed inner space into which a working fluid is injected, the working fluid being evaporated and condensed within the inner space due to heat of the light source unit, and emitting the heat of the light source unit to the outside through repeated phase changes according to evaporation and condensation of the working fluid.