A high-density plasma processing apparatus includes a processing chamber, having a susceptor for supporting an object to be processed positioned therein and a dielectric window positioned on the processing chamber to form an upper surface of the processing chamber. A reaction gas injection device injects a reaction gas into an interior of the processing chamber. An inductively coupled plasma (ICP) antenna, which is installed on a center of the dielectric window, transfers radio frequency (RF) power from an RF power supply to the interior of the processing chamber. A waveguide guides a microwave generated by a microwave generator. A circular radiative tube, which is installed on the dielectric window around the ICP antenna and is connected to the waveguide, radiates a microwave toward the interior of the processing chamber via a plurality of slots formed through a bottom wall of the radiative tube.