PLASMA DEVICE

In a plasma device 30 that emits an electromagnetic wave to a combustion chamber 10 of an engine 20 so as to generate electromagnetic wave plasma thereby igniting mixture gas, fuel efficiency for lean burn mixture combustion of an engine 20 is improved. During a flame propagation after the mixture gas is ignited in the combustion chamber, the electromagnetic wave is emitted to the combustion chamber 10 so that electrons in a propagating flame resonate with the electromagnetic wave. The resonance between the electrons in the propagating flame and the electromagnetic wave increases flame propagation speed.