PURPOSE: To enable microwave thermal plasma to be industrially utilized be applying microwave electric power to a TE011 cavity resonator, and running gas flow to a central section so as to generate the thermal plasma.

CONSTITUTION: In a metallic cavity resonator 1 for performing TE011 type resonance with respect to input microwave electric power, a rectangular waveguide 2 is attached to the side wall of the resonator, and the electric power of an exterior microwave generating source is injected thereinto through a connecting hole 3. Carrier gas and reactant are forced to flow through a central tube 4, and the same kind of gas as the carrier gas is injected into an outside tube 5 from an injection port 7. Coolant having small loss and large cooling effect is forced to flow through a space between insulating tubes 5, 6. When the interiors of the tubes are set at a low pressure, for example, at 0.1Torr, or an impulse wave high electric field is applied thereto by a Tesla coil or the like, glow discharge is generated inside the tubes, and then, microwave inductive circulating flow flows in the gas fluid so as to generate plasma flame 10. Therefore, large electric power can be easily utilized.