PURPOSE: To suppress vibration with a circuit separator in simple construction by forming the surface of a resonator from a material having greater electric resistance than Cu.

CONSTITUTION: A slit 17 is formed in a part of a circuit separator 16, and a resonator 18 using this slitted part as part of the resonance system is provided in conjugation with the slit 17, and the surface of this resonator 18 is formed from a material 19 having a greater electric resistance than Cu. In case the modulation signal component of the microwave band is included in the circulated electron stream, a high frequency electric field is generated in this slitted part, and microwave energy is generated. The microwave energy unnecessary for a crossing electromagnetic field amplifier tube is excited in this slit 17, and microwave energy is generated at the resonator 18 of magnetron type, which is made within this resonator, and the accumulated microwave energy generates resistance loss at the surface of the resonator with large electric resistance, which will be converted into thermal energy.