PURPOSE: To make the vacuum evaporation of semi-metal material more stable and obtain and electron tube with a photoelectric surface with high sensitivity by providing the temperature measurement of the semi-metal evaporation inside the electron tube.

CONSTITUTION: In the vicinity of a semi-metal evaporation source 1, an infrared snsor 16, for example, a semiconductor element that uses the photoconductive effect and whose resistance value is reduced when the infrared rays from a heated evaporation source are incident, is provided at a position where the vacuum evaporated film of antimony 3 is not applied and is connected to a measuring instrument 17. Since the temperature of the evaporation source measured using such a sensor 16 can be also externally detected by the melted state oe antimony 3, the evaporation source temperature can be predicted and controlled so that the above temperature may not rise up to a temperature at which the eutectic mixture of the antimony 3 and a boat 2 is produced in the first place, and the Sb vacuum evaporation speed when a photoelectric surface is formed can almost constantly be controlled to a desired value based on those data related to the preset experimentally measured evaporation source temperature and the calibrated Sb vacuum evaporation speed, in the second place, by interlocking said temperature with the evaporation source power supply 6.