PURPOSE: To prevent tube discharge and a defect of dark current for improving reliability by giving vibration and impact to a magnetron while impressing specific high voltage between a positive pole and a negative pole under the cold conditions.

CONSTITUTION: High voltage of then odd KV is impressed under the cold conditions between a positive pole and a negative pole of a magnetron to give vibration and impact to the magnetron for performing aging. In this way, foreign substances in a tube are made to float as much as possible in the tube and these are introduced into a high electric field to be ionized by high voltage sparks and sputtered in a part inside of the tube so as not to be floating. Thereby tube discharge and a defect of dark current are prevented to remarkably improve quality assurance and reliability after delivery.