To reduce a length in a longitudinal direction of a mixer, and to provide a mixer that is attachable even in a small space for mounting. The mixer comprises an electromagnetic wave input terminal 6 configured to receive the electromagnetic wave from the electromagnetic wave oscillator, a high voltage pulse input terminal 5 provided separately from the electromagnetic wave input terminal 6 and configured to receive the high voltage pulse from the high voltage pulse generator, a high voltage pulse output terminal 50 configured to output the electromagnetic wave and the high voltage pulse to the ignition device, an electromagnetic wave leakage prevention means 3 arranged between the high voltage pulse input terminal 5 and the high voltage pulse output terminal 50 and arranged in an axis similar with both the terminals, an insulator 4 surrounding the electromagnetic wave leakage prevention means 3 and the high voltage pulse output terminal 50, a cylindrical conductive member surrounding a part of the insulator 4, the cylindrical conductive member forming a resonator 2 connected to the electromagnetic wave input terminal 6, an inner conductor member 6a of the electromagnetic wave input terminal 6 is exposed toward an annular space 20 inside the resonator 2, and an impedance matching adjuster 7 is arranged inside the resonator 2.