An illumination apparatus includes a case, a plurality of oscillators configured to generate electromagnetic waves, and housed in the case and arranged two-dimensionally, a window unit configured to emit therefrom the electromagnetic waves, and disposed on a first side of the case, a plurality of inflow holes configured to allow fluid to flow into the case, and disposed at positions at which the electromagnetic waves from the window unit propagate, and a discharging unit configured to discharge the fluid, which has flowed into the case, out of the case, and disposed on a second side of the case, which is an opposite side to the first side. When the oscillator is viewed from the window unit, a part of the oscillator is located on an inner side of the inflow hole, and the fluid which has flowed into the case through the inflow hole reaches the oscillator.