[TASK] To achieve stabilization of ignition, improvement of flame propagation speed, improvement of output, exhaust gas cleaning, stable ignition of non-uniform mixture, improvement of fuel consumption rate, and so forth by making it possible to perform stable and highly efficient combustion/reaction even when fuel ratio of mixture is decreased and combustion/reaction of the lean mixture is performed in a heat engine such as a reciprocating engine, a rotary engine, a jet engine, and a gas turbine, or a plasma equipment. [MEANS FOR RESOLUTION] Dielectric constant control means for controlling dielectric constant of mixture in a combustion/reaction chamber 8 by introducing water and/or exhaust gas into the combustion/reaction chamber 8, a microwave radiation antenna 1 for radiating the microwave into the combustion/reaction chamber 8, and a discharge unit 2 for igniting the mixture in the combustion/reaction chamber 8 are provided. The dielectric constant control means controls the dielectric constant of the mixture before the combustion/reaction of the mixture is carried out so that resonance frequency of the mixture corresponds to frequency of the microwave.