In the magnetron, an upper end hat 122A is used as a composing element of a cathode structure member 12A and includes a portion 122Aa which is in contact with one end portion 121a of a filament coil 121. The thickness of the portion 122Aa is reduced, whereby the portion 122Aa is held not in contact with a center lead 124. Owing to this, heat generated in the filament coil 121 can travel to the upper end hat 122A without traveling directly to the center lead 124. Therefore, even when the quantity of input power is reduced to such a degree as to be able to reduce noise, or even when the electron radiation area of the filament coil 121 is reduced, the getter effect can be displayed fully. As a result of this, noise reduction and cost reduction can be realized at the same time.