Disclosed is a cooling device of a microwave oven which can be easily assembled on a rear wall of a microwave oven with reduced noise, improved cooling efficiency, and increased space efficiency of a machine chamber thereof. The cooling device has a fan cover disposed on the rear wall and having a plurality of pores formed therein. Side panels of the fan cover extend inward with such an inclination that the inner surfaces of the side panels confront a cooling fan. The fan cover protrudes backward from the machine chamber, and has a dent replacing a separate spacer for ensuring the introduction of air through the pores regardless of the place at which the microwave oven is installed.
