An electron tube includes a housing having a window having an electromagnetic wave transmitting property, an electron emission plate disposed inside the housing, the electron emission plate emitting electrons, and a holding member disposed inside the housing and configured to hold the electron emission plate and to apply a voltage to the electron emission plate. The electron emission plate has a first main surface and a second main surface facing each other. The holding member has a base portion being in contact with the first main surface, and a plurality of electron emission plate biasing portions which are in contact with an edge of the second main surface and are configured to elastically bias the electron emission plate to the base portion. The holding member is electrically connected to the second main surface through the plurality of electron emission plate biasing portions.