PURPOSE: To prevent the decrease in laser output due to unstable discharge and discharge transfer of cathode electrodes caused for a long period, by forming an oxide layer or layer an insulating film layer comprising glass, enamel and the like on the surfaces of a supporting leads for supporting the cathode electrodes.

CONSTITUTION: In a sealed type CO2 laser oscillator tube, supporting flanges 6 and 7, bellows 8 and 9, cathode electrodes 4 and 5 and mirrors 10 and 11 are arranged at both ends of an insulating tube 1 comprising glass and the like, and an anode electrode 12 is provided at the central part. In this oscillating tube, an oxide layers or insulating film layers 14 comprising glass, enamel and the like are formed on the surfaces of supporting leads 2 and 3 for supporting the cathodes 4 and 5. Even if discharging is generated between the anode 12 and the cathodes 4 and 5, the discharging parts on the cathodes 4 and 5 are not transferred to the supporting lead parts since the surfaces of the supporting leads 2 and 3 are covered with the insulating film layers 14. Therefore, the discharge is stable for a long period, and the decreases in laser output due to the outflow or adsorption of the gas caused by the discharge transfer to the supporting lead parts is prevented.