The present invention is an organic halogen compound decomposition device which utilizes a plasma, wherein a stable and reliable ignition at operation commencement is possible, and where following ignition, a good plasma form can be maintained and stable operation is possible. The organic halogen compound decomposition device is equipped with a cylindrical waveguide 7 made up of an outer conductor 8 and an inner conductor 9, and a dual construction discharge tube 5 made up of an inner tube 11 and an outer tube 12 which is provided inside the cylindrical waveguide 7 and on an identical axis. Furthermore, a probe antenna 9a formed from an extension of the inner conductor 9 is positioned so as to encircle the discharge tube 5, and the tip of the inner tube 11 is positioned further inwards than the tip of the probe antenna 9a.