PURPOSE: To eliminate poor emission at a high accuracy immediately after the exhausting of a magnetron detecting it depending on a difference between an emission current and that after the heating of an anode when a fixed filament voltage equivalent to 80W90% of the rated value is applied to the magnetron.

CONSTITUTION: A magnetron 4 is mounted on a conveyor line 5. An emission current at the first station 6 is measured with a peak current measuring device 17. When the emission current at the station 6 is less than the standard value, the magnetron 4 is removed as defective. The magnetron 4 which passed the standard at the station 6 is shifted to the station 7, at which the filament voltage is set at a fixed value between 80% and 90% of the rated value. The filament current may be at a fixed value in stead of the filament voltage. The anode voltage shall be set at such a value that the anode loss is equal to the normal service requirement.