Abstract: Disclosed is an LED illumination device of a simple configuration, capable of suppressing thermal resistance to a low level, and of effectively dissipating heat generated from LED elements. Rigidity of a mounting plate is ensured by a wall of a certain height, and thereby the mounting plate now becomes possible to endure saturation vapor pressure of a coolant liquid possibly exerted thereon, and vacuum state or near-vacuum state when the coolant liquid is injected, without being deformed. Since the rigidity of the mounting plate is ensured by the wall, a wall composing a bottom face of recesses may now be thinned, and this is advantageous in view of allowing the heat generated from the LED elements to effectively conduct to the coolant liquid, and of effectively cooling the LED elements.