Electron tube

An electron tube comprising:

• a cathode that emits thermoelectrons;
• an anode comprising a plurality of anode pieces arranged, so as to surround the cathode, in an anode cylinder inside an anode cylindrical structure, wherein a cavity resonator is formed between the anode pieces;
• an input portion to which a cathode lead to apply an input voltage to the cathode is drawn out;
• an output portion that emits microwaves excited in the cavity resonator outside;
• and
• a waveguide that transmits the microwaves emitted from the output portion,
• wherein a sealable shield casing that surrounds a part of the cathode lead is joined onto the outside surface of the anode cylindrical structure on the input portion side,
• wherein the waveguide that is sealable is joined onto the outside surface of the anode cylindrical structure on the output portion side, and
• wherein the anode cylindrical structure has a communication hole comprising a first opening that opens to an area surrounded by the shield casing and a second opening that opens to an interior of the waveguide.