PURPOSE: To stabilize the output adjustment over a wide range, by providing one anode on the projection part formed at the position biased from the center of a laser tube having a cathode in the eighborhood of the both ends to position two variable power sources between these electrodes for laser emission.

CONSTITUTION: The anode 21 is provided in the projection part 19 formed biased e.g. to the left from the center of a glass encloser 18 with cathodes 21 provided respectively in the neighborhood of the glass encloser 18. Then, the power sources E1 and E2 are connected between one anode 20 and right-left cathodes 21 being variable to apply impressed voltage. Laser light is emitted by discharge in the glass encloser. Thus, the output adjustment is stabilized over a wide range.