PURPOSE: To obtain a secondary-electron multiplier device with a long life by melting many glass bars made of glass corroded by an etching agent at their cores, corroding after providing a protective layer to block the corrosion on one surface of a cut-out glass plate, and again corroding after removing the protective layer.

CONSTITUTION: A glass bar 2 to serve as a core and to be melted by an etching agent is prepared, and the glass bar 2 is inserted into a glass tube 1 containing lead, which is then heated and extended. Thousands of these glass fibers are bundled, heated and extended. Further, thousands of them are bundled and melted to obtain a glass bar assembly 3 with a diameter of 25mm. The assembly 3 is cut at a right angle to the glass bar to cut out a glass plate 4. A protective layer 5 to block the corrosion is formed on one surface of the glass plate 4, which is immersed in an etching agent to corrode the cores. Next, after removing the protective layer 5, it is again immersed and processed in the etching agent. The resistance of a lead resistance layer 7a thus formed can be made low as compared with that of a resistance layer 7b on the side formed with the protective layer 5. A secondary-electron multiplier device is thus assembled and an image intensifier tube with a long life can be obtained.