Provided is a projection device including an illumination system, an optical engine module, a projection lens, at least one first case, at least one second case, and at least one optical element. The at least one first case includes a first flow channel to transmit a first fluid therein. The at least one second case is connected to the at least one first case to form an accommodating space. The at least one optical element is disposed in the accommodating space. Heat generated by the at least one optical element is transferred, by the first fluid, to an outside of the at least one first case.