PURPOSE: To enable to extend the pressure measuring range of cold cathode discharge type vacuum meter to higher vacuum and to enable to measure the vacuum under strong magnetic field such as the plasma enclosing unit by using this magnetic field.

CONSTITUTION: The openong 4a is provided at the cathode near the discharge space in which discharge curent flows, the ion trap electrode 11 is placed near the opening 4a at the opposed side to the anode 3, and the power supply 12 keeping the electrode 11 at positive potential Vi against the cathode and the circuit 13 measuring the current flowing to the electrode 11 are provided. Further, the current limit element or the current limit circuit 14 such as resistor in which the current limit circuit is given and it is inserted for double safety to the high voltage power supply 8, is attached. A part of ions at the discharge space flows to the electrode 11 through the opening 4a of the cathode. The rate of the number of flowing depends on the discharge voltage, magnetic field, size of opening, electrode and potential Vi. By measuring the current Ii flowing to the electrode 11, the vacuum can be measured.