PURPOSE: To perform a measurement of superhigh vacuum and high vacuum, by a method wherein a discharge in a hollow part is controlled through the installation of an electrode having a hollow part, an electrode covering an opening, a linear electrode on the axis of the hollow part, and a coil generating a magnetic line parallel to the axis.

CONSTITUTION: A hollow cylindrical anode 1, and cathode 3, 4 covering the opposite ends of the anode are placed in a vacuum vessel 5, and a linear control electrode 9 is located on a center axis of a cylinder, the electrode being coupled to a power source through conductive paths 6, 7, and 12. An electromagnetic coil 8a outside the vacuum vessel 5 is charged with current to form a magnetic field in a direction of a center axis. A DC high voltage + Va is applied to the anode 1, and a DC high voltage -VK to the cathodes 3 and 4. One end of a control power source 26 is connected to the control electrode 9 to apply a voltage Vg, and the other end is earthed through a measuring indication circuit 22. The control voltage, having a relation of Vg1>Vg3> vg2, is applied in the order of Vg1→Vg2→Vg3→Vg1, and a discharge, starting at the Vg2, is held stable up to the terminal of the Vg3 to be stopped at the Vg1. During the discharge, currents Ia, Ig, Kk, having a correlation to a degree of vacuum having a stable value, are flowed. This permits the measurement of superhigh vacuum and high vacuum from the current values.