Abstract: A housing rotatably supports a hollow drum on substantially a horizontal axis whereby articles to be treated tumble around the interior of the drum when the latter is rotated. A microwave power mechanism, such as a magnetron, is provided in a door for the housing and has an output portion thereof directed into the drum for heating and drying articles tumbling in the drum. An output portion of the microwave power mechanism has a dielectric dome-like shield mounted over it for deflecting tumbling articles away from such output. A forced air system is provided for ventilating the interior of the drum, and such system includes a passageway extending adjacent to the power mechanism so that such ventilating air also cools the power means.