An electron tube comprising: an envelope having an axis formed with a photocathode at a predetermined part of the internal surface thereof; a fixing plate which is disposed in the envelope and which includes a base having a central position located on the axis and a outer periphery surrounding the central position; an electron-bombarded semiconductor device which is fixed to the central position of the fixing plate and which faces the photocathode; a first tubular wall which is fixed to a position between the central position and the outer periphery of the fixing plate, the first tubular wall surrounding the semiconductor device and extending toward the photocathode; an evaporation source (17, 19) generating metal vapor, the evaporation source (17, 19) being disposed inside the envelope on the photocathode side relative to the fixing plate and being disposed at a position between the first tubular wall and an imaginary-extended-curved-surface of the outer periphery of the fixing plate that extends from the outer periphery toward the photocathode in parallel to the axis, the semiconductor device detecting photoelectrons emitted from the photocathode in response to an incident light thereon; a cap covering the base from above and having a circular cap shape with its central axis located on the axis, the cap having an inner wall forming the first tubular wall, an outer wall, and a ceiling that connects the inner wall and outer wall, a through-hole being formed in the center of the ceiling; a cover located above the electron-bombarded semiconductor device and disposed within the through-hole of the cap, the cover having a circular cap shape having a central axis coinciding with the axis, the cover having a ceiling, the outer periphery of the cover being connected to the inner wall of the cap and a through-hole being formed in the ceiling of the cover, such that the cover and inner wall isolate the electron-bombarded semiconductor device from the evaporation source (17, 19), the electron-bombarded semiconductor device being covered by the cover and exposed through the through-hole such that the incident direction of electrons is restricted; wherein: electrodes are arranged on the base, wire heaters are connected to corresponding electrodes, through-holes are formed in the ceiling and the evaporation source (17, 19) is held by the wire heaters and is located within the through-holes (75, 77). an envelope having an axis formed with a photocathode at a predetermined part of the internal surface thereof; a fixing plate which is disposed in the envelope and which includes a base having a central position located on the axis and a outer periphery surrounding the central position; an electron-bombarded semiconductor device which is fixed to the central position of the fixing plate and which faces the photocathode; a first tubular wall which is fixed to a position between the central position and the outer periphery of the fixing plate, the first tubular wall surrounding the semiconductor device and extending toward the photocathode; an evaporation source (17, 19) generating metal vapor, the evaporation source (17, 19) being disposed inside the envelope on the photocathode side relative to the fixing plate and being disposed at a position between the first tubular wall and an imaginary-extended-curved-surface of the outer periphery of the fixing plate that extends from the outer periphery toward the photocathode in parallel to the axis, the semiconductor device detecting photoelectrons emitted from the photocathode in response to an incident light thereon; a cap covering the base from above and having a circular cap shape with its central axis located on the axis, the cap having an inner wall forming the first tubular wall, an outer wall, and a ceiling that connects the inner wall and outer wall, a through-hole being formed in the center of the ceiling; a cover located above the electron-bombarded semiconductor device and disposed within the through-hole of the cap, the cover having a circular cap shape having a central axis coinciding with the axis, the cover having a ceiling, the outer periphery of the cover being connected to the inner wall of the cap and a through-hole being formed in the ceiling of the cover, such that the cover and inner wall isolate the electron-bombarded semiconductor device from the evaporation source (17, 19), the electron-bombarded semiconductor device being covered by the cover and exposed through the through-hole such that the incident direction of electrons is restricted; wherein: electrodes are arranged on the base, wire heaters are connected to corresponding electrodes, through-holes are formed in the ceiling and the evaporation source (17, 19) is held by the wire heaters and is located within the through-holes (75, 77). electrodes are arranged on the base, wire heaters are connected to corresponding electrodes, through-holes are formed in the ceiling and the evaporation source (17, 19) is held by the wire heaters and is located within the through-holes (75, 77).