PROBLEM TO BE SOLVED: To stabilize ignition, improve flame propagation speed, improve output, purify exhaust gas, stably ignite a non-uniform air-fuel mixture, improve a fuel consumption rate, or the like, by performing stable and highly-efficient combustion and reaction, even if a rate of fuel in an air-fuel mixture is lowered to burn and react a lean air-fuel mixture, in a heat engine such as a reciprocating engine, a rotary engine, a jet engine and a gas turbine, or a plasma device.SOLUTION: The following cycle is repeated. After a microwave is radiated from a microwave radiation antenna 1 into a combustion/reaction chamber 8 to thereby perform plasma discharge in the combustion/reaction chamber 8, a discharge section 2 performs discharge and ignition with respect to the air-fuel mixture, and then, the microwave is radiated from the microwave radiation antenna 1 into the combustion/reaction chamber 8 to thereby perform the plasma discharge within a combustion/reaction area.
