PURPOSE: To monitor the degree of vacuum visually even if a vacuum apparatus is connected to high potential by forming a fluorescent material layer to be acted by an electric field increasing in accordance with the rise of the degree of vacuum close to the vacuum apparatus.

CONSTITUTION: A pair of electrodes 1, 2 are arranged in a shield 7 and a vacuum monitoring device 8 is arranged on the outside of the shield 7. The layer of an electroluminescent fluorescent material 9 is formed on the surface of a glass plate 10 provided with an electrode 11. When a pressure in a vacuum case is low, the voltage between the shield 7 and the electrode 11 is low, so that an electric field applied to the fluorescent material 9 is low and light is not almost emitted. When the pressure is increased, the voltage between the shield 7 and the electrode 11 is increased and the fluorescent material 9 emits light. The emitted light is guided to a photoelectrical conversion element 14 through the transparent electrode 11 and the output of the element 14 is measured by a detector 16 through a resistor 15. The degree of vacuum is detected from the detected fluorescent intensity.