In an image intensifier comprising an evacuated envelope which comprises a cylindrical vessel, an input window member airtightly sealed to one end of the vessel, and an output container formed at the other end of the vessel, at least said one end portion of the cylindrical vessel is formed of metal, the input window member has a multilayer structure including an outer thin plate formed of metal weldable to the metal which constitutes at least said one end portion of the cylindrical vessel and an inner thin plate formed of aluminum or aluminum alloy which is thicker than the outer thin plate, the peripheral portion of the inner thin plate is pressure-bonded to an inner portion of a flange at the one end portion of the cylindrical vessel, and the peripheral portion of the outer thin plate extends beyond the peripheral portion of the inner thin plate and is fused with an outer portion of the flange.