ELECTRON TUBE

An electron tube (1) comprises: a housing (10) having a window (11a) that transmits electromagnetic waves; an electron discharge plate (21) that is disposed inside the housing (10), and that discharges electrons upon receiving electromagnetic waves; and a retention member (22) that is disposed inside the housing (10), that retains the electron discharge plate (21), and that applies a voltage to the electron discharge plate (21). The electron discharge plate (21) has a first primary surface (21a) and a second primary surface (21b) that oppose each other. The retention member (22) has a base section (25) that is in contact with the first primary surface (21a), and a plurality of electron discharge plate biasing sections (27c) that are in contact with an edge of the second primary surface (21b) and that elastically bias the electron discharge plate (21) to the base section (25). The retention member (22) is electrically connected to the second primary surface (21b) through the plurality of electron discharge pla